Clinical promise of next-generation complement therapeutics

The complement system and kidney cancer: pathogenesis to clinical applications

Kidney cancer poses unique clinical challenges because of its resistance to conventional treatments and its tendency to metastasize. The kidney is particularly susceptible to dysfunction of the complement system, an immune network that tumors often exploit. Recent discoveries have highlighted that the complement system not only plays a crucial role in immune surveillance and defense in the circulatory system, but also functions intracellularly and autonomously. This concept has shifted the focus of investigation toward understanding how complement proteins influence cancer progression by regulating the tumor microenvironment (TME), cell signaling, proliferation, metabolism, and the immune response. With the complement system and its inhibitors emerging as a promising new class of immunotherapeutics and potential complement-targeted treatments advancing through development pipelines and clinical trials, this Review provides a timely examination of how harnessing the complement system could lead to effective tumor treatments and how to strategically combine complement inhibitors with other cancer treatments, offering renewed hope in the fight against kidney cancer.

Red blood cells undergo lytic programmed cell death involving NLRP3

The canonical complement-mediated lysis of mature red blood cells (RBCs) leads to severe pathogenesis. However, inhibition strategies targeting complement are not always as efficient as expected, indicating that unknown mechanisms are awaiting elucidation. In this study, we investigate the intracellular events in mature RBCs following complement activation. The collected evidence demonstrates that complement-induced hemolysis is a caspase-8-dependent programmed RBC death. Furthermore, short NLRP3 (miniNLRP3) fragments in RBCs are identified to engage in the assembly of NLRP3-apoptosis-associated speck-like protein containing a CARD (ASC)-caspase-8 complex. Activated caspase-8 directly induces the proteolysis of β-spectrin, thereby disrupting the skeletal network of the RBC membrane, a process we refer to as spectosis. Spectosis signaling is also activated in autoimmune hemolytic anemia or paroxysmal nocturnal hemoglobinuria, and the inhibition of spectosis significantly reduced complement-induced hemolysis. These findings reveal a programmed death cascade in mature RBCs, which may have important implications for the treatment of hemolytic disorders.

The complement system in clinical oncology: Applications, limitations and challenges

The complement system, a key component of innate immunity, is involved in seemingly contradictory aspects of tumor progression and cancer therapy. It can act as an immune effector against cancer and modulate the antitumor activity of certain therapeutic antibodies, but it can also contribute to a tumor-promoting microenvironment. Understanding this dual role should lead to the development of better therapeutic tools, strategies for cancer treatment and biomarkers for the clinical management of cancer patients. Here, we review recent advances in the understanding of the role of complement in cancer, focusing on how these findings are being translated into the clinic. We highlight the activity of therapeutic agents that modulate the complement system, as well as combination therapies that integrate complement modulation with existing therapies. We conclude that the role of complement activation in cancer is a rapidly evolving field with the potential to translate findings into new therapeutic strategies and clinically useful biomarkers.

Blocking activation of the C1r zymogen defines a novel mode of complement inhibition

Many hematophagous organisms secrete inhibitors of the coagulation and complement systems as constituents of their salivary fluid. Whereas previous studies on salivary gland extracts from the sandfly Lutzomyia longipalpis identified SALO (salivary anticomplement from L. longipalpis) as a potent inhibitor of the classical complement pathway (CP), its precise mechanism of action has remained elusive. Here, we show that SALO inhibits the CP by binding selectively to the C1r zymogen. Using surface plasmon resonance, we found that SALO expressed by human embryonic kidney 293(T) cells (eSALO-WT) bound with nanomolar affinity to the zymogen of complement protease C1r (pro-C1r), but that it did not bind the enzymatically active form of C1r. To gain insight into the structural basis for CP inhibition by SALO, we solved a 3.3 Å resolution crystal structure of eSALO-WT bound to a recombinant form of C1r that was engineered to remain in a zymogen-like state (zC1r-12SP). eSALO-WT formed extensive interactions with the zymogen activation loop of zC1r-12SP, including groups derived from residues R463 and I464, which compose its scissile peptide bond. Although the interactions with R463 and I464 were mediated by side-chain sulfation of eSALO-WT at position Y51, we found that this modification enhanced the potency of SALO but was not required for its activity. Consistent with our structural observations, subsequent studies showed that eSALO-WT binding to pro-C1r blocked its activation and thereby inhibited the CP in hemolytic assays of complement function. Together, our results define a new mode of inhibiting complement by blocking the farthest upstream enzymatic reaction of the CP.

Inflammatory responses revealed through HIV infection of microglia-containing cerebral organoids

Cerebral organoids (COs) are valuable tools for studying the intricate interplay between glial cells and neurons in brain development and disease, including HIV-associated neuroinflammation. We developed a novel approach to generate microglia containing COs (CO-iMs) by co-culturing hematopoietic progenitors and inducing pluripotent stem cells. This approach allowed for the differentiation of microglia within the organoids concomitantly with the neuronal progenitors. Compared with conventional COs, CO-iMs were more efficient at generating CD45+/CD11b+/Iba-1+ microglia and presented a physiologically relevant proportion of microglia (~ 7%). CO-iMs presented substantially increased expression of microglial homeostatic and sensome markers as well as markers for the complement cascade. CO-iMs are susceptible to HIV infection, resulting in a significant increase in several pro-inflammatory cytokines/chemokines, which are abrogated by the addition of antiretrovirals. Thus, CO-iM is a robust model for deciphering neuropathogenesis, neuroinflammation, and viral infections of brain cells in a 3D culture system.

Preclinical safety and efficacy of the recombinant CR1 drug product CSL040 in rats and cynomolgus monkeys

CSL040 is a soluble, recombinant fragment of the complement receptor 1 (CR1) extracellular domain that acts as an inhibitor of all three pathways of the complement system. Systemic toxicity, toxicokinetics (TK), and pharmacodynamics (PD) of CSL040 were assessed in two-week intravenous (IV) bolus studies in Han Wistar rats and cynomolgus monkeys. Recovery from any effects was evaluated during a four-week recovery period. Daily repeat-dose administration for 2 weeks at doses of up to 500 mg/kg CSL040 IV was well tolerated in rats and cynomolgus monkeys, leading to a no observed adverse effect level (NOAEL) of 500 mg/kg for both species. Safety pharmacology parameters such as electrophysiology of the heart, blood pressure, heart rate, and respiratory rate measurements, and general toxicological readouts were considered unaffected by CSL040 treatment. Anti-drug antibodies (ADAs) were observed in all cynomolgus monkeys and in some rats at the highest dose of CSL040, but with no effect on pharmacokinetics (PK), supportive of adequate exposure levels as required for a safety assessment. All three complement pathways were inhibited dose-dependently by CSL040. Additionally, no effect on cytokine levels by CSL040 was detected in vitro using a cytokine release assay. These non-clinical studies with CSL040 demonstrated PD activity consistent with its mode of action, adequate PK properties, and a safety profile supporting a phase 1 clinical strategy. A small follow-up study comparing the PK/PD effects of CSL040 following IV and subcutaneous (SC) administration also suggested that the latter route of administration might be a viable alternative to IV administration.

Dynamic Complement Protein Changes in Aqueous Humor and Plasma of Patients With Retinal Vein Occlusion During Ranibizumab Treatment

Purpose

To assess dynamic changes of complement protein in aqueous humor (AH) and plasma of retinal vein occlusion (RVO) patients during ranibizumab treatment, and to explore the differential expression of complement proteins in branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO).

Patients and Methods

This prospective, consecutive case series study collected AH and plasma samples from 27 RVO patients at baseline, 1 and 2 months after ranibizumab treatment, including 19 BRVO and 8 CRVO patients. The concentrations of 13 complement proteins and vascular endothelial growth factor A (VEGF-A) were measured using Luminex® × MAP® technology.

Results

During ranibizumab treatment, a reduction in the levels of C1q (p < 0.001), C2 (p = 0.030), C4 (p = 0.001), C4b (p = 0.026), C3b/iC3b (p < 0.001), C5 (p = 0.007), C5a (p = 0.005), CFD (p = 0.022), CFH (p < 0.001), and CFI (p < 0.001) in AH was observed. No significant changes were observed in the plasma levels of all measured factors. At baseline, CRVO had higher levels of C4 (p = 0.003), C4b (p < 0.001), C3b/iC3b (p < 0.001), C5 (p = 0.020), C5a (p = 0.007), CFD (p = 0.002), CFH (p < 0.001), and CFI (p < 0.001) in AH compared to BRVO.

Conclusion

Ranibizumab treatment reduced the intraocular but not circulating activation of classical and alternative complement pathways in RVO patients. Differences in intraocular complement proteins were observed between BRVO and CRVO patients, which may reflect different pathogenesis.

FastCCC: A permutation-free framework for scalable, robust, and reference-based cell-cell communication analysis in single cell transcriptomics studies

Detecting cell-cell communications (CCCs) in single-cell transcriptomics studies is fundamental for understanding the function of multicellular organisms. Here, we introduce FastCCC, a permutation-free framework that enables scalable, robust, and reference-based analysis for identifying critical CCCs and uncovering biological insights. FastCCC relies on fast Fourier transformation-based convolution to compute p -values analytically without permutations, introduces a modular algebraic operation framework to capture a broad spectrum of CCC patterns, and can leverage atlas-scale single cell references to enhance CCC analysis on user-collected datasets. To support routine reference-based CCC analysis, we constructed the first human CCC reference panel, encompassing 19 distinct tissue types, over 450 unique cell types, and approximately 16 million cells. We demonstrate the advantages of FastCCC across multiple datasets, most of which exceed the analytical capabilities of existing CCC methods. In real datasets, FastCCC reliably captures biologically meaningful CCCs, even in highly complex tissue environments, including differential interactions between endothelial and immune cells linked to COVID-19 severity, dynamic communications in thymic tissue during T-cell development, as well as distinct interactions in reference-based CCC analysis.

Complement C3 knockout protects photoreceptors in the sodium iodate model

Complement factor 3 (C3) has emerged as a primary therapeutic target in age-related macular degeneration (AMD) supported by genetic, histologic, and clinical trial evidence. Yet, the site(s) of action are unclear. The purpose of this study was to test the effect of C3 knockout on photoreceptors and retinal pigment epithelial cells (RPE) in the sodium iodate (NaIO3) model, which mirrors some features of AMD. C3-/- and WT mice, both on a C57Bl/6J background, were injected intraperitoneally with 25 mg/kg NaIO3. Electroretinography and optical coherence tomography were performed 7 days later to assess retinal function and structure, respectively. Then, mice were euthanized for retinal immunohistochemistry, quantitative real-time PCR and enzyme-linked immunosorbent assays. NaIO3 increased C3 protein levels in the neural retina but not RPE. WT but not C3-/- mice showed NaIO3-induced iC3b deposition on photoreceptor outer segments. C3-/- mice were partially protected against photoreceptor layer thinning. There was partial preservation of rod and cone function in the C3-/- group. Neither RPE structure nor function was protected. These results suggest outer segment opsonization contributes to photoreceptor death in this model, and that targeting C3 can protect photoreceptor structure and function when RPE cells are stressed.

Identification and Validation of a Novel Prognostic Signature of Gastric Cancer Based on Seven Complement System-Related Genes: An Integrated Analysis

The complement system (CS) is linked to the progression of gastric cancer (GC), which has a high mortality rate, though its mechanisms in GC remain unclear. This study aims to identify CS-related prognostic genes with causal links to GC, and to investigate their mechanisms. The intersection between differentially expressed genes (DEGs) obtained from the TCGA-STAD dataset and CS-related genes (CRGs) was defined as differentially expressed CRGs (DCRGs). Prognostic genes with a causal association with GC (pCDCRGs) were sequentially identified via Mendelian randomization (MR) analysis and Cox and least absolute shrinkage and selection operator (LASSO) regression analyses, followed by expression analysis. A gene signature and a nomogram were then established based on pCDCRGs and independent prognostic factors. Subsequent analyses focused on functional enrichment, immune relevance, drug sensitivity, gene interactions, and molecular regulatory networks. Eventually, reverse transcription-quantitative PCR (RT-qPCR) was employed to validate expression of pCDCRGs. DCRGs were obtained from the intersection of 8,418 DEGs and 241 CRGs. Among 12 DCRGs with causal association (CDCRGs) with GC, 7 genes were identified as pCDCRGs, including FANCG, FANCF, F2R, C4BPA, SERPINF2, PROC, and CD59. Notably, CD59 was markedly highly expressed in the normal group, whereas the other genes were markedly highly expressed in the GC group. Afterward, an accurate pCDCRG signature was developed. Risk score, age, and stage were recognized as independent risk factors, and the constructed nomogram demonstrated strong predictive accuracy. Additionally, analyses indicated that these 7 pCDCRGs may influence GC by affecting pathways such as complement and coagulation cascades, immune cell infiltration, immune characteristics, immunotherapy responses, and drug sensitivity. These effects may be linked to gene interactions and the regulatory roles of lncRNAs like RMRP and miRNAs such as hsa-mir-613. RT-qPCR showed C4BPA, PROC, F2R, and SERPINF2 were markedly up-regulated, whereas CD59 was markedly down-regulated in GC tissues. This study identified seven complement system-related prognostic genes with causal links to GC, based on which we developed a highly predictive 7-pCDCRG signature, providing valuable insights for clinical prognostic prediction and immunotherapy in GC patients.

Complement-targeted therapeutics: Are we there yet, or just getting started?

Therapeutic interventions in the complement system, a key immune-inflammatory mediator and contributor to a broad range of clinical conditions, have long been considered important yet challenging or even unfeasible to achieve. Almost 20 years ago, a spark was lit demonstrating the clinical and commercial viability of complement-targeted therapies. Since then, the field has experienced an impressive expansion of targeted indications and available treatment modalities. Currently, a dozen distinct complement-specific therapeutics covering several intervention points are available in the clinic, benefiting patients suffering from eight disorders, not counting numerous clinical trials and off-label uses. Observing this rapid rise of complement-targeted therapy from obscurity to mainstream with amazement, one might ask whether the peak of this development has now been reached or whether the field will continue marching on to new heights. This review looks at the milestones of complement drug discovery and development achieved so far, surveys the currently approved drug entities and indications, and ventures a glimpse into the future advancements yet to come.

Integrated Applied Clinical Pharmacology in the Advancement of Rare and Ultra-Rare Disease Therapeutics

The introduction of safe and effective rare/ultra-rare disease treatments is a focus of many biotherapeutic enterprises. Despite this increased activity, a significant unmet need remains, and the responsibility to meet this need is augmented by enhanced genomic, biologic, medical, analytical, and informatic tools. It is recognized that the development of an effective and safe rare/ultra-rare disease therapeutic faces a number of challenges with an important role noted for clinical pharmacology. Clinical pharmacology is foundationally an integrative discipline which must be embedded in and is interdependent upon understanding the pathogenic biology, clinical presentation, disease progression, and end-point assessment of the disease under study. This manuscript presents an overview and two case examples of this integrative approach, the development of C5-targeted therapeutics for the treatment of generalized myasthenia gravis and asfotase alpha for the treatment of hypophosphatasia. The two presented case examples show the usefulness of understanding the biological drivers and clinical course of a rare disease, having relevant animal models, procuring informative natural history data, importing assessment tools from relevant alternative areas, and using integrated applied clinical pharmacology to inform target engagement, dose, and the cascade of pharmacodynamic and clinical effects that follow. Learnings from these programs include the importance of assuring cross-validation of assays throughout a development program and continued commitment to understanding the relationship among the array of Pd end points and clinical outcomes. Using an integrative approach, substantive work remains to be done to meet the unmet needs of patients with rare/ultra-rare disease.

Recruiting the Immune System against Pathogenic Bacteria Using High-Affinity Chimeric Tags

The immune system plays a critical role in protecting the host against pathogens. However, mechanisms for evading the immune system have evolved in pathogens, altering their surface proteins or causing the expression of enzymes that interfere with the immune response. These strategies cause pathogens to escape detection and destruction by the immune system, thereby inducing severe infections. Thus, there is a critical need to develop new chemical tools to recruit the immune system against evading pathogens. Here, we describe a novel strategy for targeting pathogens, by labeling them with a chimeric agent that comprises a peptide bacterial binder, conjugated to an immune-protein tag that is recognizable by the complement system, thereby recruiting the immune system against the targeted pathogen. The chimeric tag was developed by conjugating the peptide bacterial binder with the C3b complement system activating protein. We showed that the chimeric C3b tag preserved its activity and was able to bind the C5 complement protein with strong binding affinity. Using this approach, we have demonstrated that the chimeric agent was able to eradicate 90% of complement-resistant E. coli bacterial cells. By showing enhancement of complement sensitivity in complement-resistant pathogens, this work demonstrates the basis for a new therapeutic approach for targeting pathogenic bacteria, which could open a new era in the development of selective and effective antimicrobial agents.

New treatment strategies in Myasthenia gravis

Myasthenia gravis (MG) is a chronic autoimmune neuromuscular disorder characterized by muscle weakness and fatigue. The disease is primarily caused by antibodies targeting acetylcholine receptors (AChR) and muscle-specific kinase (MuSK) proteins at the neuromuscular junction. Traditional treatments for MG, such as acetylcholinesterase inhibitors, corticosteroids, and immunosuppressants, have shown efficacy but are often associated with significant long-term side effects and variable patient response rates. Notably, approximately 15% of patients exhibit inadequate responses to these standard therapies. Recent advancements in molecular therapies, including monoclonal antibodies, B cell-depleting agents, complement inhibitors, Fc receptor antagonists, and chimeric antigen receptor (CAR) T cell-based therapies, have introduced promising alternatives for MG treatment. These novel therapeutic approaches offer potential improvements in targeting specific immune pathways involved in MG pathogenesis. This review highlights the progress and challenges in developing and implementing these molecular therapies. It discusses their mechanisms, efficacy, and the potential for personalized medicine in managing MG. The integration of new molecular therapies into clinical practice could significantly transform the treatment landscape of MG, offering more effective and tailored therapeutic options for patients who do not respond adequately to traditional treatments. These innovations underscore the importance of ongoing research and clinical trials to optimize therapeutic strategies and improve the quality of life for individuals with MG.

Complement C5/C5a in the diagnosis and treatment of Graves ophthalmopathy: A Mendelian randomized study

OBJECTIVES

Graves' ophthalmopathy is a complex organ-specific autoimmune disease with an unclear pathogenesis. Complement component 5/5a (C5/C5a), a key element of the component system, may play a significant role in the disease's pathological process. This study aims to investigate the causal relationship between C5/C5a and Graves' ophthalmopathy using Mendelian randomization (MR) to provide new theoretical insights for its diagnosis and treatment.

METHODS

Utilizing summary data from genome-wide association study (GWAS), C5/C5a was designated as the exposure factor and Graves' ophthalmopathy as the outcome. The causal relationship between C5/C5a and Graves' ophthalmopathy was analyzed, and colocalization analysis was performed to determine the posterior probability of hypothesis (PPH) and verify the genetic association between C5 and Graves' ophthalmopathy.

RESULTS

The Wald ratio model showed a significant positive correlation between C5 and Graves' ophthalmopathy (OR=4.109, 95% CI 1.990 to 8.486, P<0.001). Similarly, the inverse variance weighted (IVW) model showed a positive correlation between C5a and Graves' ophthalmopathy (OR=2.901, 95% CI 1.225 to 6.869, P=0.015). Colocalization analysis showed that C5 and Graves' ophthalmopathy share a single nucleotide polymorphism (SNP), rs7036980, within the specified genetic window, with a PPH4 value of 0.81 (a value >0.80 indicates high probability).

CONCLUSIONS

Elevated levels of C5/C5a significantly increase the risk of developing Graves' ophthalmopathy. Targeting complement C5 with inhibitors may effectively reduce the risk of Graves' ophthalmopathy.

DNA methylome analysis reveals epigenetic alteration of complement genes in advanced metabolic dysfunction-associated steatotic liver disease

BACKGROUND/AIMS

Blocking the complement system is a promising strategy to impede the progression of metabolic dysfunction-associated steatotic liver disease (MASLD). However, the interplay between complement and MASLD remains to be elucidated. This comprehensive approach aimed to investigate the potential association between complement dysregulation and the histological severity of MASLD.

METHODS

Liver biopsy specimens were procured from a cohort comprising 106 Korean individuals, which included 31 controls, 17 with isolated steatosis, and 58 with metabolic dysfunction-associated steatohepatitis (MASH). Utilizing the Infinium Methylation EPIC array, thorough analysis of methylation alterations in 61 complement genes was conducted. The expression and methylation of nine complement genes in a murine MASH model were examined using quantitative RT-PCR and pyrosequencing.

RESULTS

Methylome and transcriptome analyses of liver biopsies revealed significant (P<0.05) hypermethylation and downregulation of C1R, C1S, C3, C6, C4BPA, and SERPING1, as well as hypomethylation (P<0.0005) and upregulation (P<0.05) of C5AR1, C7, and CD59, in association with the histological severity of MASLD. Furthermore, DNA methylation and the relative expression of nine complement genes in a MASH diet mouse model aligned with human data.

CONCLUSION

Our research provides compelling evidence that epigenetic alterations in complement genes correlate with MASLD severity, offering valuable insights into the mechanisms driving MASLD progression, and suggests that inhibiting the function of certain complement proteins may be a promising strategy for managing MASLD.

Pharmacokinetics, pharmacodynamics, safety, and tolerability of a single-dose riliprubart, an anti-C1s humanized monoclonal antibody in East-Asian adults: results from a Phase 1, randomized, open-label trial

OBJECTIVES

This Phase 1 trial was planned to investigate the pharmacokinetics (PK), pharmacodynamics (PD), safety, and tolerability of a single dose of riliprubart in healthy East-Asian adult participants.

METHODS

A single-center, parallel-group, randomized, open-label, single-dose study was performed to evaluate the PK, PD, safety, and tolerability of riliprubart (50 mg/kg intravenous [IV] or 600 mg subcutaneous [SC]) in 37 healthy East-Asian (Chinese, Japanese, and Korean) participants.

RESULTS

Riliprubart was slowly absorbed after SC administration (median tmax: 7.01-10.48 days) and showed a long half-life after IV or SC administration (mean: 9.52-11.0 weeks), with a bioavailability of 74.6% after SC administration. The PD profiles, which are evaluated by classical complement pathway activity or CH50, were similar and largely overlapped across East-Asian participants after a single IV or SC dose. Riliprubart was safe and well tolerated in participants following a single IV or SC dose.

CONCLUSIONS

Riliprubart was safe and well tolerated and demonstrated favorable PK and PD profiles in healthy East-Asian participants following a single IV or SC dose. These results are comparable to first-in-human study results from non-East-Asian participants and support the same dosing regimen of riliprubart for global simultaneous clinical development.

CLINICAL TRIAL REGISTRATION

This trial is registered at https://cris.nih.go.kr (identifier: KCT0006571).

Antibodies and complement are key drivers of thrombosis

Venous thromboembolism (VTE) is a common, deadly disease with an increasing incidence despite preventive efforts. Clinical observations have associated elevated antibody concentrations or antibody-based therapies with thrombotic events. However, how antibodies contribute to thrombosis is unknown. Here, we show that reduced blood flow enabled immunoglobulin M (IgM) to bind to FcμR and the polymeric immunoglobulin receptor (pIgR), initiating endothelial activation and platelet recruitment. Subsequently, the procoagulant surface of activated platelets accommodated antigen- and FcγR-independent IgG deposition. This leads to classical complement activation, setting in motion a prothrombotic vicious circle. Key elements of this mechanism were present in humans in the setting of venous stasis as well as in the dysregulated immunothrombosis of COVID-19. This antibody-driven thrombosis can be prevented by pharmacologically targeting complement. Hence, our results uncover antibodies as previously unrecognized central regulators of thrombosis. These findings carry relevance for therapeutic application of antibodies and open innovative avenues to target thrombosis without compromising hemostasis.

Immunodeficiency: Complement disorders

The complement system is an important component of innate and adaptive immunity that consists of three activation pathways. The classic complement pathway plays a role in humoral immunity, whereas the alternative and lectin pathways augment the innate response. Impairment, deficiency, or overactivation of any of the known 50 complement proteins may lead to increased susceptibility to infection with encapsulated organisms, autoimmunity, hereditary angioedema, or thrombosis, depending on the affected protein. Classic pathway defects result from deficiencies of complement proteins C1q, C1r, C1s, C2, and C4, and typically manifest with features of systemic lupus erythematosus and infections with encapsulated organisms. Alternative pathway defects due to deficiencies of factor B, factor D, and properdin may present with increased susceptibility to Neisseria infections. Lectin pathway defects, including Mannose-binding protein-associated serine protease 2 (MASP2) and ficolin 3, may be asymptomatic or lead to pyogenic infections and autoimmunity. Complement protein C3 is common to all pathways, deficiency of which predisposes patients to severe frequent infections and glomerulonephritis. Deficiencies in factor H and factor I, which regulate the alternative pathway, may lead to hemolytic uremic syndrome. Disseminated Neisseria infections result from terminal pathway defects (i.e., C5, C6, C7, C8, and C9). Diagnosis of complement deficiencies involves screening with functional assays (i.e., total complement activity [CH50], alternative complement pathway activity [AH50], enzyme-linked immunosorbent assay [ELISA]) followed by measurement of individual complement factors by immunoassay. Management of complement deficiencies requires a comprehensive and individualized approach with special attention to vaccination against encapsulated bacteria, consideration of prophylactic antibiotics, treatment of comorbid autoimmunity, and close surveillance.

Astrocyte-secreted C3 signaling impairs neuronal development and cognition in autoimmune diseases

Neuromyelitis optica (NMO) arises from primary astrocytopathy induced by autoantibodies targeting the astroglial protein aquaporin 4 (AQP4), leading to severe neurological sequelae such as vision loss, motor deficits, and cognitive decline. Mounting evidence has shown that dysregulated activation of complement components contributes to NMO pathogenesis. Complement C3 deficiency has been shown to protect against hippocampal neurodegeneration and cognitive decline in neurodegenerative disorders (e.g., Alzheimer's disease, AD) and autoimmune diseases (e.g., multiple sclerosis, MS). However, whether inhibiting the C3 signaling can ameliorate cognitive dysfunctions in NMO remains unclear. In this study, we found that the levels of C3a, a split product of C3, significantly correlate with cognitive impairment in our patient cohort. In response to the stimulation of AQP4 autoantibodies, astrocytes were activated to secrete complement C3, which inhibited the development of cultured neuronal dendritic arborization. NMO mouse models exhibited reduced adult hippocampal newborn neuronal dendritic and spine development, as well as impaired learning and memory functions, which could be rescued by decreasing C3 levels in astrocytes. Mechanistically, we found that C3a engaged with C3aR to impair neuronal development by dampening β-catenin signalling. Additionally, inhibition of the C3-C3aR-GSK3β/β-catenin cascade restored neuronal development and ameliorated cognitive impairments. Collectively, our results suggest a pivotal role of the activation of the C3-C3aR network in neuronal development and cognition through mediating astrocyte and adult-born neuron communication, which represents a potential therapeutic target for autoimmune-related cognitive impairment diseases.

A Histological Analysis and Detection of Complement Regulatory Protein CD55 in SARS-CoV-2 Infected Lungs

BACKGROUND

A complement imbalance in lung alveolar tissue can play a deteriorating role in COVID-19, leading to acute respiratory distress syndrome (ARDS). CD55 is a transmembrane glycoprotein that inhibits the activation of the complement system at the intermediate cascade level, blocking the activity of the C3 convertase.

OBJECTIVE

In our study, lung specimens from COVID-19 and ARDS-positive COVID+/ARDS+ patients were compared with COVID-19 and ARDS-negative COVID-/ARDS- as well as COVID-/ARDS+ patients.

METHODS

Histochemical staining and immunolabeling of CD55 protein were performed.

RESULTS

The COVID-/ARDS- specimen showed higher expression and homogeneous distribution of glycosaminoglycans as well as compactly arranged elastic and collagen fibers of the alveolar walls in comparison to ARDS-affected lungs. In addition, COVID-/ARDS- lung tissues revealed stronger and homogenously distributed CD55 expression on the alveolar walls in comparison to the disrupted COVID-/ARDS+ lung tissues.

CONCLUSIONS

Even though the collapse of the alveolar linings and the accumulation of cellular components in the alveolar spaces were characteristic of COVID+/ARDS+ lung tissues, evaluating CD55 expression could be relevant to understand its relation to the disease. Furthermore, targeting CD55 upregulation as a potential therapy could be an option for post-infectious complications of COVID-19 and other inflammatory lung diseases in the future.

HIV-1 infection promotes neuroinflammation and neuron pathogenesis in novel microglia-containing cerebral organoids

Cerebral organoids (COs) are a valuable tool to study the intricate interplay between glial cells and neurons in brain development and disease, including HIV-associated neuroinflammation. We developed a novel approach to generate microglia containing COs (CO-iMs) by co-culturing hematopoietic progenitors and induced pluripotent stem cells. This approach allowed for the differentiation of microglia within the organoids concomitantly to the neuronal progenitors. CO- iMs exhibited higher efficiency in generation of CD45 + /CD11b + /Iba-1 + microglia cells compared to conventional COs with physiologically relevant proportion of microglia (∼7%). CO-iMs exhibited substantially higher expression of microglial homeostatic and sensome markers as well as markers for the complement cascade. CO-iMs showed susceptibility to HIV infection resulting in a significant increase in several pro-inflammatory cytokines/chemokines and compromised neuronal function, which were abrogated by addition of antiretrovirals. Thus, CO-iM is a robust model to decipher neuropathogenesis, neurological disorders, and viral infections of brain cells in a 3D culture system.

The Inflammatory Response Induced by Aspergillus fumigatus Conidia Is Dependent on Complement Activation: Insight from a Whole Blood Model

INTRODUCTION

We aimed to elucidate the inflammatory response of Aspergillus fumigatus conidia in a whole-blood model of innate immune activation and to compare it with the well-characterized inflammatory reaction to Escherichia coli.

METHODS

Employing a human lepirudin whole-blood model, we analyzed complement and leukocyte activation by measuring the sC5b-9 complex and assessing CD11b expression. A 27-multiplex system was used for quantification of cytokines. Selective cell removal from whole blood and inhibition of C3, C5, and CD14 were also applied.

RESULTS

Our findings demonstrated a marked elevation in sC5b-9 and CD11b post-A. fumigatus incubation. Thirteen cytokines (TNF, IL-1β, IL-1ra, IL-4, IL-6, IL-8, IL-17, IFNγ, MCP-1, MIP-1α, MIP-1β, FGF-basic, and G-CSF) showed increased levels. A generally lower level of cytokine release and CD11b expression was observed with A. fumigatus conidia than with E. coli. Notably, monocytes were instrumental in releasing all cytokines except MCP-1. IL-1ra was found to be both monocyte and granulocyte-dependent. Pre-inhibiting with C3 and CD14 inhibitors resulted in decreased release patterns for six cytokines (TNF, IL-1β, IL-6, IL-8, MIP-1α, and MIP-1β), with minimal effects by C5-inhibition.

CONCLUSION

A. fumigatus conidia induced complement activation comparable to E. coli, whereas CD11b expression and cytokine release were lower, underscoring distinct inflammatory responses between these pathogens. Complement C3 inhibition attenuated cytokine release indicating a C3-level role of complement in A. fumigatus immunity.

Design and Biological Evaluation of the Long-Acting C5-Inhibited Ornithodoros moubata Complement Inhibitor (OmCI) Modified with Fatty Acid

Disorder of complement response is a significant pathogenic factor causing some autoimmune and inflammation diseases. The Ornithodoros moubata Complement Inhibitor (OmCI), a small 17 kDa natural protein, was initially extracted from soft tick salivary glands. The protein was found binding to complement C5 specifically, inhibiting the activation of the complement pathway, which is a successful therapeutic basis of complement-mediated diseases. However, a short half-life due to rapid renal clearance is a common limitation of small proteins for clinical application. In this study, we extended the half-life of OmCI by modifying it with fatty acid, which was a method used to improve the pharmacokinetics of native peptides and proteins. Five OmCI mutants were initially designed, and single-site cysteine mutation was introduced to each of them. After purification, four OmCI mutants were obtained that showed similar in vitro biological activities. Three mutants of them were subsequently coupled with different fatty acids by nucleophilic substitution. In total, 15 modified derivatives were screened and tested for anticomplement activity in vitro. The results showed that coupling with fatty acid would not significantly affect their complement-inhibitory activity (CH50 and AH50). OmCIT90C-CM02 and OmCIT90C-CM05 were validated as the applicable OmCI bioconjugates for further pharmacokinetic assessments, and both showed improved plasma half-life in mice compared with unmodified OmCI (15.86, 17.96 vs 2.57 h). In summary, our data demonstrated that OmCI conjugated with fatty acid could be developed as the potential long-acting C5 complement inhibitor in the clinic.

Complement regulation in the eye: implications for age-related macular degeneration

Careful regulation of the complement system is critical for enabling complement proteins to titrate immune defense while also preventing collateral tissue damage from poorly controlled inflammation. In the eye, this balance between complement activity and inhibition is crucial, as a low level of basal complement activity is necessary to support ocular immune privilege, a prerequisite for maintaining vision. Dysregulated complement activation contributes to parainflammation, a low level of inflammation triggered by cellular damage that functions to reestablish homeostasis, or outright inflammation that disrupts the visual axis. Complement dysregulation has been implicated in many ocular diseases, including glaucoma, diabetic retinopathy, and age-related macular degeneration (AMD). In the last two decades, complement activity has been the focus of intense investigation in AMD pathogenesis, leading to the development of novel therapeutics for the treatment of atrophic AMD. This Review outlines recent advances and challenges, highlighting therapeutic approaches that have advanced to clinical trials, as well as providing a general overview of the complement system in the posterior segment of the eye and selected ocular diseases.

Balancing efficacy and safety of complement inhibitors

Complement inhibitors have been approved for several immune-mediated diseases and they are considered the next paradigm-shifting approach in the treatment of glomerulonephritis. The hierarchical organization of the complement system offers numerous molecular targets for therapeutic intervention. However, complement is an integral element of host defense and therefore complement inhibition can be associated with serious infectious complications. Here we give a closer look to the hierarchical complement system and how interfering with proximal versus distal or selective versus unselective molecular targets could determine efficacy and safety. Furthermore, we propose to consider the type of disease, immunological activity, and patient immunocompetence when stratifying patients, e.g., proximal/unselective targets for highly active and potentially fatal diseases while distal and selective targets may suit more chronic disease conditions with low or moderate disease activity requiring persistent complement blockade in patients with concomitant immunodeficiency. Certainly, there exists substantial promise for anti-complement therapeutics. However, balancing efficacy and safety will be key to establish powerful treatment effects with minimal adverse events, especially when complement blockade is continued over longer periods of time in chronic disorders.

Membranoproliferative Glomerulonephritis Pattern of Injury

Membranoproliferative glomerulonephritis (MPGN) is no longer a disease but a pattern of injury in various diseases. Characterized by electron-dense deposits, mesangial proliferation, and duplication of the glomerular basement membrane, MPGN was previously classified by findings seen by electron microscopy. However, recognizing complement dysfunction in relation to cases with the MPGN pattern of injury substantially changed our view of its pathogenesis. A new classification, including immune complex-mediated and complement-mediated MPGN, has become preferable and has been adopted by international guidelines. Despite these advancements, accurate diagnosis of MPGN remains a clinical challenge, given the pathological and clinical similarities between immune complex-mediated and complement-mediated MPGN. Additional testing, such as molecular and genetic testing, is often necessary. Here, we will summarize our current understanding of the MPGN pattern of injury from a pathology perspective as an introductory article in the following chapters.

PolySialic Acid Nanoparticles Actuate Complement-Factor-H-Mediated Inhibition of the Alternative Complement Pathway: A Safer Potential Therapy for Age-Related Macular Degeneration

The alternative pathway of the complement system is implicated in the etiology of age-related macular degeneration (AMD). Complement depletion with pegcetacoplan and avacincaptad pegol are FDA-approved treatments for geographic atrophy in AMD that, while effective, have clinically observed risks of choroidal neovascular (CNV) conversion, optic neuritis, and retinal vasculitis, leaving room for other equally efficacious but safer therapeutics, including Poly Sialic acid (PSA) nanoparticle (PolySia-NP)-actuated complement factor H (CFH) alternative pathway inhibition. Our previous paper demonstrated that PolySia-NP inhibits pro-inflammatory polarization and cytokine release. Here, we extend these findings by investigating the therapeutic potential of PolySia-NP to attenuate the alternative complement pathway. First, we show that PolySia-NP binds CFH and enhances affinity to C3b. Next, we demonstrate that PolySia-NP treatment of human serum suppresses alternative pathway hemolytic activity and C3b deposition. Further, we show that treating human macrophages with PolySia-NP is non-toxic and reduces markers of complement activity. Finally, we describe PolySia-NP-treatment-induced decreases in neovascularization and inflammatory response in a laser-induced CNV mouse model of neovascular AMD. In conclusion, PolySia-NP suppresses alternative pathway complement activity in human serum, human macrophage, and mouse CNV without increasing neovascularization.

Discovery and Characterization of a New Class of C5aR1 Antagonists Showing In Vivo Activity

C5a is an anaphylatoxin protein produced by the cleavage of the complement system's component C5 protein. It signals through the G-protein-coupled receptor C5a receptor 1 (C5aR1) to induce the chemotaxis of primarily neutrophils and monocytes and the release of inflammatory molecules. A large body of evidence linking C5aR1 signaling to acute and chronic inflammatory disorders has triggered interest in developing potent C5aR antagonists. Herein we report the discovery of new C5aR1 antagonistic chemical classes. Many representatives showed low nanomolar IC50 values in a C5aR1 β-arrestin-2 recruitment assay, inhibiting the migration of human neutrophils toward C5a and the internalization of the receptor in human whole blood. Two leading compounds were characterized further in vivo. Target engagement of the receptor by these two C5aR1 antagonists was demonstrated in vivo. In particular, the inhibition of migration in vitro with the two compounds further translated in a dose-dependent efficacy in a rat model of C5a-induced neutrophilia.

Inhibition of acute complement responses towards bolus-injected nanoparticles using targeted short-circulating regulatory proteins

Effective inhibition of the complement system is needed to prevent the accelerated clearance of nanomaterials by complement cascade and inflammatory responses. Here we show that a fusion construct consisting of human complement receptor 2 (CR2) (which recognizes nanosurface-deposited complement 3 (C3)) and complement receptor 1 (CR1) (which blocks C3 convertases) inhibits complement activation with picomolar to low nanomolar efficacy on many types of nanomaterial. We demonstrate that only a small percentage of nanoparticles are randomly opsonized with C3 both in vitro and in vivo, and CR2-CR1 immediately homes in on this subpopulation. Despite rapid in vivo clearance, the co-injection of CR2-CR1 in rats, or its mouse orthologue CR2-Crry in mice, with superparamagnetic iron oxide nanoparticles nearly completely blocks complement opsonization and unwanted granulocyte/monocyte uptake. Furthermore, the inhibitor completely prevents lethargy caused by bolus-injected nanoparticles, without inducing long-lasting complement suppression. These findings suggest the potential of the targeted complement regulators for clinical evaluation.

Myasthenia gravis: the changing treatment landscape in the era of molecular therapies

Myasthenia gravis (MG) is an autoimmune disorder that affects the neuromuscular junction, leading to muscle weakness and fatigue. MG is caused by antibodies against the acetylcholine receptor (AChR), the muscle-specific kinase (MuSK) or other AChR-related proteins that are expressed in the postsynaptic muscle membrane. The standard therapeutic approach for MG has relied on acetylcholinesterase inhibitors, corticosteroids and immunosuppressants, which have shown good efficacy in improving MG-related symptoms in most people with the disease; however, these therapies can carry a considerable burden of long-term adverse effects. Moreover, up to 15% of individuals with MG exhibit limited or no response to these standard therapies. The emergence of molecular therapies, including monoclonal antibodies, B cell-depleting agents and chimeric antigen receptor T cell-based therapies, has the potential to revolutionize the MG treatment landscape. This Review provides a comprehensive overview of the progress achieved in molecular therapies for MG associated with AChR antibodies and MuSK antibodies, elucidating both the challenges and the opportunities these therapies present to the field. The latest developments in MG treatment are described, exploring the potential for personalized medicine approaches.

Complement C3 as a potential drug target in periodontitis: Evidence from the cis-Mendelian randomization approach

AIM

Evidence from a Phase IIa trial showed that a complement C3-targeted drug reduced gingival inflammation in patients with gingivitis. Using drug-target Mendelian randomization (MR), we investigated whether genetically proxied C3 inhibition alters the risk of periodontitis.

MATERIALS AND METHODS

We used multiple 'cis' instruments from the vicinity of the encoding loci of C3. Instrument selection was restricted to the drug target encoding loci (chromosome 19; 6,677,715-6,730,573 (GRCh37/hg19)). We selected three uncorrelated single-nucleotide polymorphisms (rs141552034, rs145406915, rs11569479) that were associated with serum C3 levels (p value <1 × 10-4 ) from a genome-wide association study (GWAS) of 5368 European descent individuals. We extracted association statistics from a GWAS of 17,353 clinical periodontitis cases and 28,210 European controls. Wald ratios were combined using inverse-variance weighted meta-analysis to estimate the odds ratio (OR) of the genetically proxied inhibition of C3 in relation to periodontitis.

RESULTS

MR analysis revealed that the inhibition of C3 reduces the odds of periodontitis (OR 0.91 per 1 standard deviation reduction in C3; 95% confidence interval 0.87-0.96, p value = .0003).

CONCLUSIONS

Findings from our MR analysis suggest a potential protective effect of C3 blockade against periodontitis.

A guide to complement biology, pathology and therapeutic opportunity

Complement has long been considered a key innate immune effector system that mediates host defence and tissue homeostasis. Yet, growing evidence has illuminated a broader involvement of complement in fundamental biological processes extending far beyond its traditional realm in innate immunity. Complement engages in intricate crosstalk with multiple pattern-recognition and signalling pathways both in the extracellular and intracellular space. Besides modulating host-pathogen interactions, this crosstalk guides early developmental processes and distinct cell trajectories, shaping tissue immunometabolic and regenerative programmes in different physiological systems. This Review provides a guide to the system-wide functions of complement. It highlights illustrative paradigm shifts that have reshaped our understanding of complement pathobiology, drawing examples from evolution, development of the central nervous system, tissue regeneration and cancer immunity. Despite its tight spatiotemporal regulation, complement activation can be derailed, fuelling inflammatory tissue pathology. The pervasive contribution of complement to disease pathophysiology has inspired a resurgence of complement therapeutics with major clinical developments, some of which have challenged long-held dogmas. We thus highlight major therapeutic concepts and milestones in clinical complement intervention.

Impact of Preanalytical Procedures on Complement Biomarkers in Cerebrospinal Fluid and Plasma from Controls and Alzheimer's Disease Patients

Background

Studies comparing cerebrospinal fluid (CSF) and plasma complement proteins in Alzheimer's disease (AD) patients versus healthy controls (HC) have yielded inconsistent results. Discrepancies in the preanalytical sample handling could contribute to the heterogeneity in the reported findings.

Objective

Using qualified immunoassays, we aimed at assessing the impact of preanalytical procedures on complement proteins in blood and CSF from AD patients and HCs.

Methods

We supplemented HC and AD CSF/plasma with complement stabilizers and measured the complement proteins C4a, C4, C3a, C3, Factor Bb and Factor B by immunoassay. We tested the impact of freeze-thaw (FT) cycles on fluid complement proteins.

Results

Most complement proteins were mildly impacted by FT cycles in plasma but not CSF, except for C3a which displayed greater sensitivity to FTs in CSF than in plasma. In CSF, the effect of FTs on C3a was reduced but not prevented by the supplementation with EDTA (±Futhan).

Conclusions

Our findings provide recommendations for CSF/plasma sample handling to ensure robust and reproducible complement biomarker analyses in AD.

Targeting synapse function and loss for treatment of neurodegenerative diseases

Synapse dysfunction and loss are hallmarks of neurodegenerative diseases that correlate with cognitive decline. However, the mechanisms and therapeutic strategies to prevent or reverse synaptic damage remain elusive. In this Review, we discuss recent advances in understanding the molecular and cellular pathways that impair synapses in neurodegenerative diseases, including the effects of protein aggregation and neuroinflammation. We also highlight emerging therapeutic approaches that aim to restore synaptic function and integrity, such as enhancing synaptic plasticity, preventing synaptotoxicity, modulating neuronal network activity and targeting immune signalling. We discuss the preclinical and clinical evidence for each strategy, as well as the challenges and opportunities for developing effective synapse-targeting therapeutics for neurodegenerative diseases.

Structure-property Relationships Reported for the New Drugs Approved in 2023

Drug-like properties play pivotal roles in drug adsorption, distribution, metabolism, excretion, and toxicity. Therefore, efficiently optimizing these properties is essential for the successful development of novel therapeutics. Understanding the structure-property relationships of clinically approved drugs can provide valuable insights for drug design and optimization strategies. Among the new drugs approved in 2023, which include 31 small-molecule drugs in the US, the structureproperty relationships of nine drugs were compiled from the medicinal chemistry literature, in which detailed information on pharmacokinetic and/or physicochemical properties was reported not only for the final drug but also for its key analogs generated during drug development. The structure- property relationships of nine newly approved drugs are summarized, including three kinase inhibitors and three G-protein-coupled receptor antagonists. Several optimization strategies, such as bioisosteric replacement and steric handle installation, have successfully produced clinical candidates with enhanced physicochemical and pharmacokinetic properties. The summarized structure- property relationships demonstrate how appropriate structural modifications can effectively improve overall drug-like properties. The ongoing exploration of structure-property relationships of clinically approved drugs is expected to offer valuable guidance for developing future drugs.

Characterization of the bispecific VHH antibody gefurulimab (ALXN1720) targeting complement component 5, and designed for low volume subcutaneous administration

The bispecific antibody gefurulimab (also known as ALXN1720) was developed to provide patients with a subcutaneous treatment option for chronic disorders involving activation of the terminal complement pathway. Gefurulimab blocks the enzymatic cleavage of complement component 5 (C5) into the biologically active C5a and C5b fragments, which triggers activation of the terminal complement cascade. Heavy-chain variable region antigen-binding fragment (VHH) antibodies targeting C5 and human serum albumin (HSA) were isolated from llama immune-based libraries and humanized. Gefurulimab comprises an N-terminal albumin-binding VHH connected to a C-terminal C5-binding VHH via a flexible linker. The purified bispecific VHH antibody has the expected exact size by mass spectrometry and can be formulated at greater than 100 mg/mL. Gefurulimab binds tightly to human C5 and HSA with dissociation rate constants at pH 7.4 of 54 pM and 0.9 nM, respectively, and cross-reacts with C5 and serum albumin from cynomolgus monkeys. Gefurulimab can associate with C5 and albumin simultaneously, and potently inhibits the terminal complement activity from human serum initiated by any of the three complement pathways in Wieslab assays. Electron microscopy and X-ray crystallography revealed that the isolated C5-binding VHH recognizes the macroglobulin (MG) 4 and MG5 domains of the antigen and thereby is suggested to sterically prevent C5 binding to its activating convertase. Gefurulimab also inhibits complement activity supported by the rare C5 allelic variant featuring an R885H substitution in the MG7 domain. Taken together, these data suggest that gefurulimab may be a promising candidate for the potential treatment of complement-mediated disorders.

Revisiting the relationship between complement and ulcerative colitis

Ulcerative colitis (UC) is an inflammatory bowel disorder (IBD) characterized by relapsing chronic inflammation of the colon that causes continuous mucosal inflammation. The global incidence of UC is steadily increasing. Immune mechanisms are involved in the pathogenesis of UC, of which complement is shown to play a critical role by inducing local chronic inflammatory responses that promote tissue damage. However, the function of various complement components in the development of UC is complex and even paradoxical. Some components (e.g. C1q, CD46, CD55, CD59, and C6) are shown to safeguard the intestinal barrier and reduce intestinal inflammation, while others (e.g. C3, C5, C5a) can exacerbate intestinal damage and accelerate the development of UC. The complement system was originally thought to function primarily in an extracellular mode; however, recent evidence indicates that it can also act intracellularly as the complosome. The current study provides an overview of current studies on complement and its role in the development of UC. While there are few studies that describe how intracellular complement contributes to UC, we discuss potential future directions based on related publications. We also highlight novel methods that target complement for IBD treatment.

New Insights into the Complement Receptor of the Ig Superfamily Obtained from Structural and Functional Studies on Two Mutants

The extracellular region of the complement receptor of the Ig superfamily (CRIg) binds to certain C3 cleavage products (C3b, iC3b, C3c) and inhibits the alternative pathway (AP) of complement. In this study, we provide further insight into the CRIg protein and describe two CRIg mutants that lack multiple lysine residues as a means of facilitating chemical modifications of the protein. Structural analyses confirmed preservation of the native CRIg architecture in both mutants. In contrast to earlier reports suggesting that CRIg binds to C3b with an affinity of ∼1 μM, we found that wild-type CRIg binds to C3b and iC3b with affinities <100 nM, but to C3c with an affinity closer to 1 μM. We observed this same trend for both lysine substitution mutants, albeit with an apparent ∼2- to 3-fold loss of affinity when compared with wild-type CRIg. Using flow cytometry, we confirmed binding to C3 fragment-opsonized Staphylococcus aureus cells by each mutant, again with an ∼2- to 3-fold decrease when compared with wild-type. Whereas wild-type CRIg inhibits AP-driven lysis of rabbit erythrocytes with an IC50 of 1.6 μM, we observed an ∼3-fold reduction in inhibition for both mutants. Interestingly, we found that amine-reactive crosslinking of the CRIg mutant containing only a single lysine results in a significant improvement in inhibitory potency across all concentrations examined when compared with the unmodified mutant, but in a manner sensitive to the length of the crosslinker. Collectively, our findings provide new insights into the CRIg protein and suggest an approach for engineering increasingly potent CRIg-based inhibitors of the AP.

Comprehensive analysis of subtypes and risk model based on complement system associated genes in ccRCC

BACKGROUND

Immune therapy is widely used in treating clear cell renal cell carcinoma (ccRCC), yet identifying patient subgroups that are expected to response remains challenging. As complement system can mediate immune effects, including the progression of tumors, a correlation between complement system and immune therapy may exist.

METHODS

Based on 11 complement system associated genes (CSAGs) identified from The Cancer Genome Atlas (TCGA), we performed unsupervised clustering and classified the tumors into two different complement system (CS) patterns. The clinical significance, tumor microenvironment (TME), functional enrichment, and immune infiltration were further analyzed. A novel scoring system named CSscore was developed based on the expression levels of the 11 CSAGs.

RESULTS

Two distinct CS patterns were identified, classified as Cluster1 and Cluster2, and Cluster1 showed poor clinical outcome. Further analysis of functional enrichment, immune cell infiltration, and genetic variation revealed that Cluster1 had high infiltration of TME immune cells, but also exhibited high immune escape. The novel prognostic model, CSscore could act as an independent prognostic factor and effectively predict patients' prognosis and distinguish the therapeutic efficacy of different immune treatment strategies. The pan-cancer analysis of the CSscore indicates its potential to be further generalized to other types of cancer.

CONCLUSIONS

Two distinct CS patterns were identified and were further analyzed in terms of infiltration of TME immune cells and immune escape, providing potential explanations for the impact on prognosis of ccRCC. Our CSscore prognostic model may offer a novel perspective in the management of ccRCC patients, and potentially other types of cancer as well.

Prognostic Model and Tumor Immune Microenvironment Analysis of Complement-Related Genes in Gastric Cancer

Introduction

The complement system is integral to the innate and adaptive immune response, helping antibodies eliminate pathogens. However, the potential role of complement and its modulators in the tumor microenvironment (TME) of gastric cancer (GC) remains unclear.

Methods

This study assessed the expression, frequency of somatic mutations, and copy number variations of complement family genes in GC derived from The Cancer Genome Atlas (TCGA). Lasso and Cox regression analyses were conducted to develop a prognostic model based on the complement genes family, with the training and validation sets taken from the TCGA-GC cohort (n=371) and the International Gene Expression Omnibus (GEO) cohort (n=433), correspondingly. The nomogram assessment model was used to predict patient outcomes. Additionally, the link between immune checkpoints, immune cells, and the prognostic model was investigated.

Results

In contrast to patients at low risk, those at high risk had a less favorable outcome. The prognostic model-derived risk score was shown to serve as a prognostic marker of GC independently, as per the multivariate Cox analysis. Nomogram assessment showed that the model had high reliability for predicting the survival of patients with GC in the 1, 3, 5 years. Additionally, the risk score was positively linked to the expression of immune checkpoints, notably CTLA4, LAG3, PDCD1, and CD274, according to an analysis of immune processes. The core gene C5aR1 in the prognostic model was found to be upregulated in GC tissues in contrast to adjoining normal tissues, and patients with elevated expressed levels of C5aR1 had lower 10-year overall survival (OS) rates.

Conclusion

Our work reveals that complement genes are associated with the diversity and complexity of TME. The complement prognosis model help improves our understanding of TME infiltration characteristics and makes immunotherapeutic strategies more effective.

Pan-Neurofascin autoimmune nodopathy - a life-threatening, but reversible neuropathy

PURPOSE OF REVIEW

Autoimmune nodopathies are immune-mediated neuropathies associated with antibodies targeting the peripheral node of Ranvier. Recently, antibodies against all neurofascin-isoforms (pan-neurofascin) have been linked to a clinical phenotype distinct from previously described autoimmune nodopathies. Here, we aim at highlighting the molecular background and the red flags for diagnostic assessment and provide treatment and surveillance approaches for this new disease.

RECENT FINDINGS

Neurofascin-isoforms are located at different compartments of the node of Ranvier: Neurofascin-186 at the axonal nodal gap, and Neurofascin-155 at the terminal Schwann cell loops at the paranode. Pan-neurofascin antibodies recognize a common epitope on both isoforms and can access the node of Ranvier directly. Depending on their subclass profile, antibodies can induce direct structural disorganization and complement activation. Affected patients present with acute and immobilizing sensorimotor neuropathy, with cranial nerve involvement and long-term respiratory insufficiency. Early antibody-depleting therapy is crucial to avoid axonal damage, and remission is possible despite extended disease and high mortality. The antibody titer and serum neurofilament light chain levels can serve as biomarkers for diagnosis and therapy monitoring.

SUMMARY

Pan-neurofascin-associated autoimmune nodopathies has unique molecular and clinical features. Testing should be considered in severe and prolonged Guillain-Barré-like phenotype.

Complement: Functions, location and implications

The complement system, an arm of the innate immune system plays a critical role in both health and disease. The complement system is highly complex with dual possibilities, helping or hurting the host, depending on the location and local microenvironment. The traditionally known functions of complement include surveillance, pathogen recognition, immune complex trafficking, processing and pathogen elimination. The noncanonical functions of the complement system include their roles in development, differentiation, local homeostasis and other cellular functions. Complement proteins are present in both, the plasma and on the membranes. Complement activation occurs both extra- and intracellularly, which leads to considerable pleiotropy in their activity. In order to design more desirable and effective therapies, it is important to understand the different functions of complement, and its location-based and tissue-specific responses. This manuscript will provide a brief overview into the complex nature of the complement cascade, outlining some of their complement-independent functions, their effects at different locale, and their implication in disease settings.

Complement-mediated immune mechanisms in allergy

Allergic conditions are associated with canonical and noncanonical activation of the complement system leading to the release of several bioactive mediators with inflammatory and immunoregulatory properties that regulate the immune response in response to allergens during the sensitization and/or the effector phase of allergic diseases. Further, immune sensors of complement and regulator proteins of the cascade impact on the development of allergies. These bioactive mediators comprise the small and large cleavage fragments of C3 and C5. Here, we provide an update on the multiple roles of immune sensors, regulators, and bioactive mediators of complement in allergic airway diseases, food allergies, and anaphylaxis. A particular emphasis is on the anaphylatoxins C3a and C5a and their receptors, which are expressed on many of the effector cells in allergy such as mast cells, eosinophils, basophils, macrophages, and neutrophils. Also, we will discuss the multiple pathways, by which the anaphylatoxins initiate and control the development of maladaptive type 2 immunity including their impact on innate lymphoid cell recruitment and activation. Finally, we briefly comment on the potential to therapeutically target the complement system in different allergic conditions.

Complement and coagulation cascades pathway-related signature as a predictor of immunotherapy in metastatic urothelial cancer

BACKGROUND

Immune checkpoint inhibitors (ICIs) have shown efficacy in patients with metastatic urothelial cancer (mUC), however, only a small subset of patients could benefit from ICIs. Identifying predictive biomarkers of ICIs in patients with mUC is clinical meaningful for patient stratification and administration.

METHODS

Clinical and transcriptomic data of mUC patients treated with ICIs from mUC cohort (IMvigor210 study) was utilized to explore the predictive biomarkers. LASSO Cox regression was performed to construct a predictive model. The predictive model was trained and tested in the mUC cohort, and then exploratively tested in clear cell renal cell carcinoma (ccRCC) and melanoma cohorts in which patients also received ICIs regimens.

RESULTS

The differentially expressed genes (DEGs) in complement and coagulation cascades pathway (CCCP) were mainly enriched in non-responders of ICIs in the mUC cohort. A CCCP risk score was constructed based on the DEGs in CCCP. Patients with a low-risk score were more responsive to ICIs and had better overall survival (OS) than those with a high-risk score in the training set (HR, 0.38; 95%CI, 0.27-0.53, P<0.001) and the test set (HR, 0.34; 95%CI, 0.17-0.71, P=0.003). The association between the CCCP risk score and OS remained significant in the multivariable cox regression by adjusting PD-L1 expression and TMB (P<0.05). In addition, there was no difference for OS in the bladder cancer patients without ICIs (TCGA-BLCA cohort, HR, 0.76, 95%CI, 0.49-1.18, P=0.22), suggesting a predictive but not prognostic effect of the risk score. For the exploratory analysis, consistent results were observed that low-risk group showed superior OS in ccRCC cohort (HR, 0.52, 95%CI, 0.37-0.75, P<0.001) and melanoma cohort (HR, 0.27, 95%CI, 0.12-0.62, P=0.001).

CONCLUSIONS

Our study showed that the CCCP risk score is an independent biomarker that predicts the efficacy of ICIs in mUC patients. The patients with a low-risk score tend to have a better response to ICIs and a longer life time probably due to the immune-activated TME. Further studies are needed to validate the clinical utility of the seven-gene signature.

Unleashing the power of complement activation: unraveling renal damage in human anti-glomerular basement membrane disease

Anti-glomerular basement membrane (GBM) disease is a rare but life-threatening autoimmune disorder characterized by rapidly progressive glomerulonephritis with or without pulmonary hemorrhage. Renal biopsies of anti-GBM patients predominantly show linear deposition of IgG and complement component 3 (C3), indicating a close association between antigen-antibody reactions and subsequent complement activation in the pathogenesis of the disease. All three major pathways of complement activation, including the classical, lectin, and alternative pathways, are involved in human anti-GBM disease. Several complement factors, such as C3, C5b-9, and factor B, show a positive correlation with the severity of the renal injury and act as risk factors for renal outcomes. Furthermore, compared to patients with single positivity for anti-GBM antibodies, individuals who are double-seropositive for anti-neutrophil cytoplasmic antibody (ANCA) and anti-GBM antibodies exhibit a unique clinical phenotype that lies between ANCA-associated vasculitis (AAV) and anti-GBM disease. Complement activation may serve as a potential "bridge" for triggering both AAV and anti-GBM conditions. The aim of this article is to provide a comprehensive review of the latest clinical evidence regarding the role of complement activation in anti-GBM disease. Furthermore, potential therapeutic strategies targeting complement components and associated precautions are discussed, to establish a theoretical basis for complement-targeted therapies.