Formation Of Membrane Attack Complex Research Articles

DNA Nanostructure-Templated Antibody Complexes Provide Insights into the Geometric Requirements of Human Complement Cascade Activation.

The classical complement pathway is activated by antigen-bound IgG antibodies. Monomeric IgG must oligomerize to activate complement via the hexameric C1q complex, and hexamerizing mutants of IgG appear as promising therapeutic candidates. However, structural data have shown that it is not necessary to bind all six C1q arms to initiate complement, revealing a symmetry mismatch between C1 and the hexameric IgG complex that has not been adequately explained. Here, we use DNA nanotechnology to produce specific nanostructures to template antigens and thereby spatially control IgG valency. These DNA-nanotemplated IgG complexes can activate complement on cell-mimetic lipid membranes, which enabled us to determine the effect of IgG valency on complement activation without the requirement to mutate antibodies. We investigated this using biophysical assays together with 3D cryo-electron tomography. Our data revealed the importance of interantigen distance on antibody-mediated complement activation, and that the cleavage of complement component C4 by the C1 complex is proportional to the number of ideally spaced antigens. Increased IgG valency also translated to better terminal pathway activation and membrane attack complex formation. Together, these data provide insights into how nanopatterning antigen-antibody complexes influence the activation of the C1 complex and suggest routes to modulate complement activation by antibody engineering. Furthermore, to our knowledge, this is the first time DNA nanotechnology has been used to study the activation of the complement system.

CFH Haploinsufficiency and Complement Alterations in Early-Onset Macular Degeneration.

Complement dysregulation is a key component in the pathogenesis of age-related macular degeneration (AMD) and related diseases such as early-onset macular drusen (EOMD). Although genetic variants of complement factor H (CFH) are associated with AMD risk, the impact of CFH and factor H-like protein 1 (FHL-1) expression on local complement activity in human retinal pigment epithelium (RPE) remains unclear. We identified a novel CFH variant in a family with EOMD and generated patient induced pluripotent stem cell (iPSC)-derived RPE cells. We assessed CFH and FHL-1 co-factor activity through C3b breakdown assays and measured complement activation by immunostaining for membrane attack complex (MAC) formation. Expression of CFH, FHL-1, local alternative pathway (AP) components, and regulators of complement activation (RCA) in EOMD RPE cells was determined by quantitative PCR, western blot, and immunostaining. Isogenic EOMD (cEOMD) RPE was generated using CRISPR/Cas9 gene editing. The CFH variant (c.351-2A>G) resulted in loss of CFH and FHL-1 expression and significantly reduced CFH and FHL-1 protein expression (∼50%) in EOMD iPSC RPE cells. These cells exhibited increased MAC deposition upon exposure to normal human serum. Under inflammatory or oxidative stress conditions, CFH and FHL-1 expression in EOMD RPE cells paralleled that of controls, whereas RCA expression, including MAC formation inhibitors, was elevated. CRISPR/Cas9 correction restored CFH/FHL-1 expression and mitigated alternative pathway complement activity in cEOMD RPE cells. Identification of a novel CFH variant in patients with EOMD resulting in reduced CFH and FHL-1 and increased local complement activity in EOMD iPSC RPE supports the involvement of CFH haploinsufficiency in EOMD pathogenesis.

Targeting terminal pathway reduces brain complement activation, amyloid load and synapse loss, and improves cognition in a mouse model of dementia

Complement is dysregulated in the brain in Alzheimer’s Disease and in mouse models of Alzheimer’s disease. Each of the complement derived effectors, opsonins, anaphylatoxins and membrane attack complex (MAC), have been implicated as drivers of disease but their relative contributions remain unclarified. Here we have focussed on the MAC, a lytic and pro-inflammatory effector, in the AppNL−G−F mouse amyloidopathy model. To test the role of MAC, we back-crossed to generate AppNL−G−F mice deficient in C7, an essential MAC component. C7 deficiency ablated MAC formation, reduced synapse loss and amyloid load and improved cognition compared to complement-sufficient AppNL−G−F mice at 8–10 months age. Adding back C7 caused increased MAC formation in brain and an acute loss of synapses in C7-deficient AppNL−G−F mice. To explore whether C7 was a viable therapeutic target, a C7-blocking monoclonal antibody was administered systemically for one month in AppNL−G−F mice aged 8–9 months. Treatment reduced brain MAC and amyloid deposition, increased synapse density and improved cognitive performance compared to isotype control-treated AppNL−G−F mice. The findings implicate MAC as a driver of pathology and highlight the potential for complement inhibition at the level of MAC as a therapy in Alzheimer’s disease.

HylS’, a fragment of truncated hyaluronidase of Streptococcus suis, contributes to immune evasion by interaction with host complement factor C3b

ABSTRACT Pathogenic bacteria have evolved many strategies to evade surveillance and attack by complements. Streptococcus suis is an important zoonotic pathogen that infects humans and pigs. Hyaluronidase (HylA) has been reported to be a potential virulence factor of S. suis. However, in this study, it was discovered that the genomic region encoding HylA of the virulent S. suis strain SC19 and other ST1 strains was truncated into four fragments when aligned with a strain containing intact HylA and possessing hyaluronidase activity. As a result, SC19 had no hyaluronidase activity, but one truncated HylA fragment, designated as HylS,’ directly interacted with complement C3b, as confirmed by western ligand blotting, pull-down, and ELISA assays. The deposition of C3b and membrane attack complex (MAC) formation on the surface of a HylS’-deleted mutant (ΔhylS’) was significantly increased compared to wild-type SC19. In human sera and whole blood, ΔhylS’ survival was significantly reduced compared to that in SC19. The resistance of ΔhylS’ to macrophages and human polymorphonuclear neutrophil PMNs also decreased. In a mouse infection model, ΔhylS’ showed reduced lethality and lower bacterial load in the organs compared to that of SC19. We conclude that the truncated hyaluronidase HylS’ fragment contributes to complement evasion and the pathogenesis of S. suis.

Plasmid-encoded toxin of Escherichia coli cleaves complement system proteins and inhibits complement-mediated lysis in vitro.

Plasmid-encoded toxin (Pet) is an autotransporter protein of the serine protease autotransporters of Enterobacteriaceae (SPATE) family, important in the pathogenicity of Escherichia coli. The pet gene was initially found in the enteroaggregative E. coli (EAEC) virulence plasmid, pAA2. Although this virulence factor was initially described in EAEC, an intestinal E. coli pathotype, pet may also be present in other pathotypes, including extraintestinal pathogenic strains (ExPEC). The complement system is an important defense mechanism of the immune system that can be activated by invading pathogens. Proteases produced by pathogenic bacteria, such as SPATEs, have proteolytic activity and can cleave components of the complement system, promoting bacterial resistance to human serum. Considering these factors, the proteolytic activity of Pet and its role in evading the complement system were investigated. Proteolytic assays were performed by incubating purified components of the complement system with Pet and Pet S260I (a catalytic site mutant) proteins. Pet, but not Pet S260I, could cleave C3, C5 and C9 components, and also inhibited the natural formation of C9 polymers. Furthermore, a dose-dependent inhibition of ZnCl2-induced C9 polymerization in vitro was observed. E. coli DH5α survived incubation with human serum pre-treated with Pet. Therefore, Pet can potentially interfere with the alternative and the terminal pathways of the complement system. In addition, by cleaving C9, Pet may inhibit membrane attack complex (MAC) formation on the bacterial outer membrane. Thus, our data are suggestive of a role of Pet in resistance of E. coli to human serum.

Incremental Burden Associated with Dose Escalation in Patients with Paroxysmal Nocturnal Hemoglobinuria Treated with Complement Inhibitors

Introduction: Paroxysmal nocturnal hemoglobinuria (PNH) is a rare blood disorder characterized by complement-mediated hemolytic anemia. Terminal complement component C5 inhibitors eculizumab (ECU) and ravulizumab (RAVU) inhibit the formation of membrane attack complex, and thereby ameliorates intravascular hemolysis in PNH. Some patients exhibit breakthrough intravascular hemolysis near the end of 14-day treatment cycle for ECU or 8-week treatment cycle for RAVU. To manage breakthrough hemolysis, different treatment strategies may be attempted in the clinical practice, including shortening the dosing interval and/or increasing the dose of ECU and RAVU. This study aimed to estimate the incremental costs associated with dose escalation in patients with PNH treated with ECU or RAVU in the US. Methods: Adult (age ≥18 years) patients with PNH (ICD-10-CM code D59.5) treated with ECU or RAVU from health plan claims data (01/01/2011 to 09/30/2022) with ≥3 months of continuous health plan coverage following the first claim for ECU or RAVU were included in this retrospective cohort study. Dosing patterns were investigated during the maintenance phase. Consistent with label-recommended dosing schedule, the maintenance phase started from day 29 and day 15 post-first claim for ECU and RAVU, respectively, until the earliest of treatment discontinuation/loss to follow-up/end of data. Dose escalation for ECU was defined as 1) an increased dose (i.e., 1,200 or 1,500 mg) and/or 2) an increased infusion frequency (i.e., ≥2 infusions within 12 days). Patient-weight information was not available; dose escalation for RAVU was defined as an increased infusion frequency (i.e., ≥2 infusions within 49 days). All-cause and PNH-related direct healthcare costs measured during maintenance phase for the overall cohort and subgroup of patients with dose escalation were assessed for ECU and RAVU separately. Incremental costs associated with dose escalation in the pre vs. post dose escalation period were assessed for ECU and RAVU separately; p-values from Wilcoxon signed-rank tests were reported. Results: A total of 278 patients treated with ECU (mean± SD age, 42±13 years; 60% female) were included in the overall cohort and a subgroup of 151 patients were observed with a dose escalation (mean±SD age, 41±13 years; 58% female). For the overall ECU cohort (N=278), during a mean follow-up of 23 months, total all-cause and PNH-related costs (mean±SD) were $67,650±$32,518 and $65,751±$31,379 per patient per month (PPPM), respectively. In the subgroup of patients with dose escalation (N=151), over a mean follow-up of 30 months, total all-cause and PNH-related costs (mean±SD) were $71,466±$33,452 and $69,471±$31,595 PPPM, respectively. In the overall cohort and subgroup of patients with dose escalation, PNH-related treatment costs represented 90% and 92% of total all-cause costs respectively. A total of 171 patients treated with RAVU (mean± SD age, 39±12 years; 43% female) were included in the overall cohort and a subgroup of 26 patients were observed with a dose escalation (i.e., increased infusion frequency only) (mean± SD age, 37±11 years; 54% female). For the overall RAVU cohort (N=171), during a mean follow-up of 17 months, total all-cause and PNH-related costs (mean±SD) were $50,779±$26,258 and $49,213±$25,751 PPPM, respectively. In the subgroup of patients with dose escalation (N=26), over a mean follow-up of 20 months, total all-cause and PNH-related costs (mean±SD) were $52,819±$20,965 and $50,740±$20,837 PPPM, respectively. In the overall cohort and subgroup of patients with dose escalation, PNH-related treatment costs represented 93% and 91% of total all-cause costs, respectively. Incremental costs (mean cost differences) associated with dose escalation for ECU were of $16,861 (p<0.01) and $15,956 (p<0.01) PPPM for all-cause and PNH-related total costs, respectively; and for RAVU were of $4,950 (p<0.05) and $3,738 (p=0.06) PPPM for all-cause and PNH-related total costs, respectively (Figures 1A and 1B). Conclusions: In this study of PNH patients treated with C5 inhibitors, dose escalation was associated with significant incremental costs for both ECU and RAVU. Further research is warranted to clarify the reasons for dose escalation, which may potentially indicate an unmet clinical need for more efficacious treatment options to help prevent breakthrough symptoms and reduce the burden of PNH.

Voluntary wheel running prevents formation of membrane attack complexes and myelin degradation after peripheral nerve injury

Regular aerobic activity is associated with a reduced risk of chronic pain in humans and rodents. Our previous studies in rodents have shown that prior voluntary wheel running can normalize redox signaling at the site of peripheral nerve injury, attenuating subsequent neuropathic pain. However, the full extent of neuroprotection offered by voluntary wheel running after peripheral nerve injury is unknown. Here, we show that six weeks of voluntary wheel running prior to chronic constriction injury (CCI) reduced the terminal complement membrane attack complex (MAC) at the sciatic nerve injury site. This was associated with increased expression of the MAC inhibitor CD59. The levels of upstream complement components (C3) and their inhibitors (CD55, CR1 and CFH) were altered by CCI, but not increased by voluntary wheel running. Since MAC can degrade myelin, which in turn contributes to neuropathic pain, we evaluated myelin integrity at the sciatic nerve injury site. We found that the loss of myelinated fibers and decreased myelin protein which occurs in sedentary rats following CCI was not observed in rats with prior running. Substitution of prior voluntary wheel running with exogenous CD59 also attenuated mechanical allodynia and reduced MAC deposition at the nerve injury site, pointing to CD59 as a critical effector of the neuroprotective and antinociceptive actions of prior voluntary wheel running. This study links attenuation of neuropathic pain by prior voluntary wheel running with inhibition of MAC and preservation of myelin integrity at the sciatic nerve injury site.

Exposure-Response Relationships between the Complement Factor B Inhibitor Iptacopan and Lactate Dehydrogenase (LDH) and Hemoglobin (Hb) in Patients (Pts) with Paroxysmal Nocturnal Hemoglobinuria (PNH)

Background: PNH is an ultrarare disease characterized by complement-mediated hemolysis and subsequent anemia, bone marrow failure and thrombosis. In pts not treated with complement inhibitors, intravascular hemolysis (IVH) results from unregulated progression of the complement system and membrane attack complex formation. IVH is controlled in pts treated with anti-C5 therapy, but extravascular hemolysis (EVH) may emerge and cause persistent anemia. High LDH levels are a marker of ongoing IVH, while anemia can result from both IVH and EVH. Iptacopan is the first oral proximal complement inhibitor targeting factor B to selectively inhibit the alternative pathway of the complement cascade. As shown in PNH Phase III trials (APPLY-PNH [NCT04558918] and APPOINT-PNH [NCT04820530]), iptacopan can achieve good control of hemolysis. Aim: To support the dose selection for iptacopan, this analysis characterizes the exposure-response relationships between iptacopan and efficacy measures (LDH and Hb) in pts with PNH. The effect of prior anti-C5 treatment status has also been evaluated. Methods: This analysis is based on data from 4 clinical trials enrolling pts with PNH.Final data were used from the completed Phase II trials X2201 (NCT03439839; pts with active hemolysis despite anti-C5 therapy received concomitant iptacopan) and X2204 (NCT03896152; anti-C5-naïve pts received iptacopan monotherapy), in which iptacopan was administered orally in doses ranging from 25 to 200 mg twice daily (bid). Data up to the cut-off dates of 26 September 2022 and 2 November 2022 were used from the Phase III trials, APPLY-PNH (pts previously treated with anti-C5) and APPOINT-PNH (pts not treated with complement inhibitors including anti-C5), respectively, in which oral iptacopan was administered at 200 mg bid. A longitudinal mixed-effects modeling approach was applied to LDH and Hb. To account for the delay between exposure and response, indirect response models were developed for LDH and Hb. The models were used to predict the long-term (6 months) LDH and Hb responses for various iptacopan bid dose levels and to estimate (using simulation) the proportion of pts achieving LDH ≤1.5 × upper limit of normal (ULN) and Hb ≥12 g/dL. Results: The modeling dataset contained 161 pts with PNH; 94 (58%) were female, and median (range) age was 45 (18-84) years. For modeling of LDH and Hb levels, 2812 and 2587 samples were used, respectively, as well as 1577 pharmacokinetic samples. In total, 53 (33%) pts had not received anti-C5 treatment. Of the remaining 108 pts, 16 (15%) received iptacopan as add-on therapy to anti-C5 (pts from X2201) and 92 (85%) had previously received anti-C5 (pts from APPLY-PNH). The indirect response models were considered biologically plausible and adequately described the data using a common EC 50 value to both anti-C5-naïve pts and pts currently receiving or who previously received anti-C5. The estimated concentration of iptacopan required to achieve 90% of the maximum response (EC 90) of LDH was 268 ng/mL (90% confidence interval [CI] 238, 302), irrespective of prior anti-C5 treatment status ( Figure). The estimated typical LDH value after iptacopan treatment at an exposure >EC 90 was 237 U/L (90% CI 224, 250) within the normal LDH range (<250 U/L). Iptacopan 200 mg bid was the dose at which the highest proportion of pts (86%) achieved LDH ≤1.5 × ULN. While baseline LDH levels differed between anti-C5-naïve pts and pts currently receiving or who previously received anti-C5, similar proportions of these pts achieved LDH ≤1.5 × ULN (84% and 88%, respectively). The estimated EC 90 of Hb ≥12 g/dL was 1968 ng/mL (90% CI 1661, 2333) ( Figure); 89% of all pts were expected to reach EC 90 exposure at iptacopan 200 mg bid. The estimated Hb value after treatment with iptacopan at an exposure >EC 90 was 12.7 g/dL (90% CI 12.4, 13.0). 70% of pts were expected to achieve Hb normalization (≥12 g/dL) with iptacopan 200 mg bid. Similar proportions of anti-C5-naïve pts and pts who were currently receiving or who previously received anti-C5 achieved Hb ≥12 g/dL (71% and 68%, respectively). Conclusions: Indirect response models were developed to describe the exposure-response relationships between iptacopan and efficacy measures (LDH and Hb) in pts with PNH. The analysis demonstrated that 200 mg bid is the dose of oral iptacopan that achieves LDH ≤1.5 × ULN and Hb normalization in the highest proportion of patients regardless of prior treatment status.

Artificial surface labelling of Escherichia coli with StrepTagII antigen to study how monoclonal antibodies drive complement-mediated killing.

Antibodies play a key role in the immune defence against Gram-negative bacteria. After binding to bacterial surface antigens, IgG and IgM can activate the complement system and trigger formation of lytic membrane attack complex (MAC) pores. Molecular studies to compare functional activity of antibodies on bacteria are hampered by the limited availability of well-defined antibodies against bacterial surface antigens. Therefore, we genetically engineered E. coli by expressing the StrepTagII antigen into outer membrane protein X (OmpX) and validated that these engineered bacteria were recognised by anti-StrepTagII antibodies. We then combined this antigen-antibody system with a purified complement assay to avoid interference of serum components and directly compare MAC-mediated bacterial killing via IgG1 and pentameric IgM. While both IgG1 and IgM could induce MAC-mediated killing, we show that IgM has an increased capacity to induce complement-mediated killing of E. coli compared to IgG1. While Fc mutations that enhance IgG clustering after target binding could not improve MAC formation, mutations that cause formation of pre-assembled IgG hexamers enhanced the complement activating capacity of IgG1. Altogether, we here present a system to study antibody-dependent complement activation on E. coli and show IgM's enhanced capacity over IgG to induce complement-mediated lysis of E. coli.

Urine Proteomics Link Complement Activation with Interstitial Fibrosis/Tubular Atrophy in Lupus Nephritis Patients

BackgroundIntrarenal complement activation has been implicated in the pathogenesis of tubulointerstitial fibrosis in lupus nephritis (LN) based on prior animal studies. The assembly of the membrane attack complex (MAC) by complement C5b to C9 on the cell membrane leads to cytotoxic pores and cell lysis, while CD59 inhibits MAC formation by preventing C9 from joining the complex. We hypothesize that complement activation and imbalance between complement activation and inhibition, as defined by increased production of individual complement components and uncontrolled MAC activation relative to CD59 inhibition, are associated with interstitial fibrosis and tubular atrophy (IFTA) in LN and correlate with the key mediators of kidney fibrosis- transforming growth factor receptors beta (TGFRβ), platelet-derived growth factor beta (PDGFβ) and platelet-derived growth factor receptor beta (PDGFRβ). MethodsWe included urine samples from 46 adults and pediatric biopsy-proven lupus nephritis patients who underwent clinically indicated kidney biopsies between 2010 and 2019. We compared individual urinary complement components and the urinary C9-to-CD59 ratio between LN patients with moderate/severe IFTA and none/mild IFTA. IFTA was defined as none/mild (<25% of interstitium affected) versus moderate/severe (≥ 25% of interstitium affected). Proteomics analysis was performed using mass spectrometry (Orbitrap Fusion Lumos, Thermo Scientific) and processed by the Proteome Discoverer. Urinary complement proteins enriched in LN patients with moderate/severe IFTA were correlated with serum creatinine, TGFβR1, TGFβR2, PDGFβ, and PDGFRβ. ResultsOf the 46 LN patients included in the study, 41 (89.1%) were women, 20 (43.5%) self-identified as Hispanic or Latino, and 26 (56.5%) self-identified as Black or African American. Ten of the 46 (21.7%) LN patients had moderate/severe IFTA on kidney biopsy. LN patients with moderate/severe IFTA had an increased urinary C9-to-CD59 ratio [median 0.91 (0.83-1.05) vs 0.81 (0.76-0.91), p=0.01]. Urinary C3 and CFI levels in LN patients with moderate/severe IFTA were higher compared to those with none/mild IFTA [C3 median (IQR) 24.4(23.5-25.5) vs. 20.2 (18.5–22.2), p= 0.02], [CFI medium (IQR) 28.8 (21.8-30.6) vs. 20.4 (18.5-22.9), p=0.01]. Complement C9, CD59, C3 and CFI correlated with TGFβR1, PDGFβ, and PDGFRβ, while C9, CD59 and C3 correlated with TGFβR2. ConclusionThis study is one of the first to compare the urinary complement profile in LN patients with moderate/severe IFTA and none/mild IFTA in human tissues. This study identified C3, CFI, and C9-to-CD59 ratio as potential markers of tubulointerstitial fibrosis in LN.

Assay Development and Measurement of Autoantibody-Mediated Complement Activity in Myasthenia Gravis

Autoantibodies against the acetylcholine receptor (AChR) play a critical role in myasthenia gravis, where autoantibody-mediated complement activation has been implicated in neuromuscular junction damage. However, the exact pathogenic role of the autoantibodies in complement activation remains unclear. We developed a cell-based assay that measures AChR autoantibody–mediated complement membrane attack complex (MAC) formation. A modified HEK293T cell line using CRISPR/Cas9 genome editing to disrupt expression of the complement regulator genes (CD46, CD55, and CD59)—was used to measure AChR autoantibody–mediated membrane attack complex (MAC) formation through flow cytometry. We observed a modest correlation between autoantibody-mediated complement mediated activity and disease burden suggesting heterogeneity in autoantibody-mediated activation of complement system.

Complement inhibition in Myasthenia – from basics to RCT data

Myasthenia gravis (MG) is the prototypic autoimmune neurological disorder causing fatiguable muscle weakness either limited to the ocular muscles or becoming generalised involving the limb and bulbar muscles. Nine out of 10 generalised MG patients have IgG1 or IgG3 antibodies against the acetylcholine receptor (AChR). AChR antibodies cause neuromuscular weakness by internalisation of AChR, receptor blockade and by activating the complement pathway. Complement activation causes formation of the membrane attack complex (MAC) leading to degradation of the neuromuscular junction (NMJ). Several animal models have confirmed the role of complement in the pathogenesis of MG, with the experimental models (EAMG) often needing complement inhibitory therapies to prevent or reverse the disease. Various molecules that target the complement system have now been developed to treat myasthenia gravis. The vast majority of the currently studied molecules target the C5 protein, thereby preventing the formation of MAC and subsequent NMJ destruction. The currently studied anti-complement therapies for MG include Eculizumab, Zilucoplan, Ravulizumab, Pozelimab, Cemdisiran, Gefurilimab, Danicopan and few others in the pipeline. Eculizumab has been shown in clinical trials to be effective in the treatment of refractory MG, but further sub-group analysis and real-life experience have shown that this can be beneficial in various patients including those receiving regular IVIG, plasma exchange or Rituximab. It was approved for use by FDA in Oct 2017. Ravulizumab is a long-acting monoclonal antibody which has similar mechanism of action to Eculizumab and was approved for use in MG by FDA in April 2022. Zilucoplan is a macrocyclic peptide which binds to C5 and C5b thus preventing terminal complement activation, which can be given subcutaneously (FDA new drug application accepted in Nov 2022). Many of these have also been shown to have long term benefit in different sub-groups of patients with MG. Patients would need to be vaccinated against Neisseria meningitidis because of the risk of Gram-negative septicaemia, although no major safety signatures have been noted in the studies so far. Future studies may be able to identify specific biomarkers which might aid in selecting the most appropriate patients who might respond to these therapies.

87 Activation of complement pathways and formation of membrane attack complex contribute to the development of severe COVID-19

87 Activation of complement pathways and formation of membrane attack complex contribute to the development of severe COVID-19

173 Roles of complement dysregulation and membrane attack complex formation in developmental synapse loss

173 Roles of complement dysregulation and membrane attack complex formation in developmental synapse loss

Complement terminal pathway inhibition reduces peritoneal injuries in a rat peritonitis model.

Peritonitis and the resulting peritoneal injuries are common problems that prevent long-term peritoneal dialysis (PD) therapy in patients with end-stage kidney diseases. Previously, we have analyzed the relationship between the complement system and progression of peritoneal injuries associated with PD, particularly focusing on the early activation pathways and effects of the anaphylatoxins. We here utilized a novel mAb 2H2 that blocks assembly of the membrane attack complex (MAC) to investigate roles of the complement terminal pathway in PD-associated peritoneal injury. We intraperitoneally injected mAb 2H2 anti-C5b-7 (2.5 or 5 mg/rat) once or twice over the five-day course of the experiment to investigate the effects of inhibiting formation of MAC in a fungal rat peritonitis model caused by repeated intraperitoneal administration of zymosan after methylglyoxal pretreatment (Zy/MGO model). Rats were sacrificed on day 5 and macroscopic changes in both parietal and visceral peritoneum evaluated. Peritoneal thickness, the abundance of fibrinogen and complement C3 and MAC deposition in tissue and accumulation of inflammatory cells were pathologically assessed. The results showed that mAb 2H2, but not isotype control mAb, reduced peritoneal thickness and accumulation of inflammatory cells in a dose and frequency-dependent manner in the Zy/MGO model. These effects were accompanied by decreased C3, MAC, and fibrinogen deposition in peritoneum. In conclusion, in the rat Zy/MGO model, complement terminal pathway activation and MAC formation substantially contributed to development of peritoneal injuries, suggesting that MAC-targeted therapies might be effective in preventing development of peritoneal injuries in humans.

Results from a first-in-human phase 1B study of a complement factor H inhibitor (GT103) in patients with non-small cell lung cancer (NSCLC).

9128 Background: GT103 is a first-in-class IgG3 monoclonal antibody that was derived from a single human B cell and inhibits complement factor H (CFH). CFH is implicated in cancer immune evasion and overexpression portends a poor prognosis in multiple malignancies. CFH regulates C3 convertase in the alternative pathway of the complement cascade, limiting downstream opsonization and membrane attack complex formation. Monoclonal antibody inhibition of CFH facilitates complement-dependent tumor cell lysis, modulates the adaptive immune response, and inhibits tumor growth. Methods: GT103 is being evaluated in a multi-institutional, first-in-human, phase Ib study in patients with advanced stage, refractory NSCLC. A standard ‘3+3’ dose escalation schema was used across four dose levels, with treatment given until disease progression or unacceptable toxicity. Dose limiting toxicity (DLT) observation period included cycle 1 and radiographic disease assessment was performed every 6 weeks. We have previously reported that no DLT was seen at the highest two dose levels of 3 mg /kg or 10 mg/kg administered IV every 3 weeks. Two expansion cohorts have now been opened at 10 mg/kg IV every 2 week and 15 mg/kg every 3 weeks dose levels allowing up to 6 patients at each dose level. We herein present updated clinical outcomes and analysis of correlative biomarkers. Results: As of February 3, 2023, twenty-five patients have been treated, with a median follow up of 230 days. Five of the 21 patients in the dose escalation cohort demonstrated stable disease by RECIST criteria. In the 10 mg/kg dose level, one patient has experienced prolonged disease stabilization and has received 12 cycles to date with tumor reduction on CT. The DLT period is ongoing for two patients enrolled in the 10 mg/kg IV every 2 weeks and two patients in the 15 mg/kg every 3 weeks expansion cohorts. Soluble C5b-9 (s C5b-9) is a candidate pharmacodynamic biomarker for GT103 and was measured at baseline and at day 15 from patients in all four dose escalation levels (0.3, 1, 3, 10 mg/kg). An increase in sC5b-9 was found in 13 of 21 patients at day 15. A marked doubling of the baseline sC5b-9 level was demonstrated in a subset of patients by day 15 indicative of biologic activity. Conclusions: GT103 is well tolerated in heavily pretreated advanced NSCLC population. Early clinical activity has been demonstrated to date with stable disease seen in 24% of patients. Updated clinical results and correlative data will be presented. A separate phase 2 study of combination GT103 with pembrolizumab is planned for patients with refractory NSCLC. Trial Registration: The study was approved by Duke University IRB with approval number Pro00104564. Clinical trial information: NCT04314089 .

Discovery of a Novel Series of Potent, Selective, Orally Available, and Brain-Penetrable C1s Inhibitors for Modulation of the Complement Pathway.

A novel series of non-amidine-based C1s inhibitors have been explored. Starting from high-throughput screening hit 3, isoquinoline was replaced with 1-aminophthalazine to enhance C1s inhibitory activity while exhibiting good selectivity against other serine proteases. We first disclose a crystal structure of a complex of C1s and a small-molecule inhibitor (4e), which guided structure-based optimization around the S2 and S3 sites to further enhance C1s inhibitory activity by over 300-fold. Improvement of membrane permeability by incorporation of fluorine at the 8-position of 1-aminophthalazine led to identification of (R)-8 as a potent, selective, orally available, and brain-penetrable C1s inhibitor. (R)-8 significantly inhibited membrane attack complex formation induced by human serum in a dose-dependent manner in an in vitro assay system, proving that selective C1s inhibition blocked the classical complement pathway effectively. As a result, (R)-8 emerged as a valuable tool compound for both in vitro and in vivo assessment.

PD19-01 C3a/C3aR1 SIGNALING AS A CRUCIAL PATHOGENIC MECHANISM IN MEMBRANOUS NEPHROPATHY

You have accessJournal of UrologyCME1 Apr 2023PD19-01 C3a/C3aR1 SIGNALING AS A CRUCIAL PATHOGENIC MECHANISM IN MEMBRANOUS NEPHROPATHY Qi Zhang, Sofia Bin, Astgik Petrosyan, Valentina Villani, Kevin Lemley, Roger de Filippo, Laura Perin, Paolo Cravedi, and Stefano da Sacco Qi ZhangQi Zhang More articles by this author , Sofia BinSofia Bin More articles by this author , Astgik PetrosyanAstgik Petrosyan More articles by this author , Valentina VillaniValentina Villani More articles by this author , Kevin LemleyKevin Lemley More articles by this author , Roger de FilippoRoger de Filippo More articles by this author , Laura PerinLaura Perin More articles by this author , Paolo CravediPaolo Cravedi More articles by this author , and Stefano da SaccoStefano da Sacco More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003285.01AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Primary membranous nephropathy (MN) is a leading cause of nephrotic syndrome in adults worldwide caused by the deposition of anti-podocyte-antibodies in the glomerular subepithelial space. While complement deposition is thought to play a crucial pathogenic role, the exact effector mechanism of complement in MN is unclear due to the lack of in vitro and in vivo systems that can faithfully recapitulate human disease. We have developed a novel glomerulus-on-a-chip system (GOAC) using human primary podocytes and glomerular endothelial cells (GEC) and assessed functional response to human MN serum, role of membrane-attack-complex (MAC) formation and C3a/C3aR1 signaling in MN pathogenesis. METHODS: GOACs were exposed to anti-PLA2R+ sera from MN patients; sera from healthy individuals were used as control. Functional response was assessed by albumin permeability assay to evaluate permselectivity. Role of PLA2R1, IgGs, complement, MAC and C3a/C3aR1 signaling pathway were assessed by immunofluorescence, western blotting and functional analysis while mechanisms of action were explored by PCR arrays, proteomics and immunostaining. Results were confirmed in vitro using podocytes on which C3aR1 was silenced and in vivo using THSD7A induced MN in balb/c mice. RESULTS: Following exposure to sera from MN patients, we confirmed lgG deposition, complement activation and MAC formation accompanied by albumin leakage. PLA2R silencing on podocytes, IgG neutralization as well as complement inactivation successfully prevented injury while leakage still occurred following MAC inhibition. GOAC supplemented with C3aR1 antagonists as well as GOAC using podocytes in which C3aR1 was silenced were able to counteract glomerular filtration damage and prevent albumin leakage and lessen oxidative stress in podocytes. Efficacy of C3aR1 antagonists in preventing proteinuria was confirmed in vivo, substantiating our findings. CONCLUSIONS: We have successfully developed a glomerulus-on-a-chip system that closely mimics the GFB structure and provides a powerful tool for studying renal regenerative and disease mechanisms in proteinuric diseases. Using a combination of in vitro and in vivo models, we showed that C3a/C3aR signaling plays a dominant role in complement-mediated MN pathogenesis. Source of Funding: NIH NIDDK © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e577 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Qi Zhang More articles by this author Sofia Bin More articles by this author Astgik Petrosyan More articles by this author Valentina Villani More articles by this author Kevin Lemley More articles by this author Roger de Filippo More articles by this author Laura Perin More articles by this author Paolo Cravedi More articles by this author Stefano da Sacco More articles by this author Expand All Advertisement PDF downloadLoading ...

Structural basis for membrane attack complex inhibition by CD59

CD59 is an abundant immuno-regulatory receptor that protects human cells from damage during complement activation. Here we show how the receptor binds complement proteins C8 and C9 at the membrane to prevent insertion and polymerization of membrane attack complex (MAC) pores. We present cryo-electron microscopy structures of two inhibited MAC precursors known as C5b8 and C5b9. We discover that in both complexes, CD59 binds the pore-forming β-hairpins of C8 to form an intermolecular β-sheet that prevents membrane perforation. While bound to C8, CD59 deflects the cascading C9 β-hairpins, rerouting their trajectory into the membrane. Preventing insertion of C9 restricts structural transitions of subsequent monomers and indirectly halts MAC polymerization. We combine our structural data with cellular assays and molecular dynamics simulations to explain how the membrane environment impacts the dual roles of CD59 in controlling pore formation of MAC, and as a target of bacterial virulence factors which hijack CD59 to lyse human cells.

Complement-dependent cytotoxicity of human autoantibodies against myelin oligodendrocyte glycoprotein.

The autoantibody to myelin oligodendrocyte glycoprotein (MOG), a component of the central nervous system myelin, has been identified in a subset of demyelinating diseases. However, there is no convincing evidence to support the direct pathogenic contribution of this autoantibody. To elucidate the role of anti-MOG autoantibodies in human demyelinating disorders, we assessed the effect of autoantibodies on MOG-expressing cells. Mammalian cells expressing the human MOG protein reacted with human anti-MOG autoantibodies in the presence or absence of complement. Sera from 86 patients and 11 healthy sera were used. We analyzed anti-MOG antibody titers, IgG subclass, and their cytotoxic ability in sera from patients with various neurological diseases. Membrane attack complex (MAC) formation was examined by detection of complement C9 or C9neo with western blot or flow cytometry. Among 86 patients, 40 were determined to be MOG-IgG-positive and 46 were negative. Anti-MOG-positive sera, but not -negative sera, caused cell death in MOG-expressing cells. This cytotoxic effect was disappeared after heat inactivation of sera. Importantly, anti-MOG IgG and externally added complement were necessary for sufficient cytotoxic effects. Anti-MOG autoantibodies were histologically colocalized with complement and formed a membrane attack complex consisting of anti-MOG IgG and complement factors. The human MOG antibody specifically killed MOG-expressing cells in vitro in the presence of externally added complement. Membrane attack complexes were formed on the cells, indicating that this autoantibody activated complement-mediated cytotoxicity. Further studies in larger numbers of patients are needed to characterize the role of complement in MOGAD.