Complement C5a and Clinical Markers as Predictors of COVID-19 Disease Severity and Mortality in a Multi-Ethnic Population

Factor B as a therapeutic target for the treatment of complement-mediated diseases

The complement system, consisting of three initiating pathways-classical, lectin and alternative, is an important part of innate immunity. Dysregulation of the complement system is implicated in the pathogenesis of several autoimmune and inflammatory diseases. Therapeutic inhibition of the complement system has been recognized as a viable approach to drug development and has been successful with the approval of a small number of complement inhibitors for diseases such as paroxysmal nocturnal hemoglobinuria, atypical hemolytic uremic syndrome, neuromyelitis optica, myasthenia gravis and geographic atrophy. More recently, therapies selectively targeting the alternative pathway (AP), which drives the amplification of the complement responses, are being evaluated for these complement-mediated diseases. Complement Factor B, a serine protease, is a unique component of the AP that is essential for the catalytic activity of AP C3 convertase and AP C5 convertase. Inhibition of Factor B blocks the activity of the alternative pathway and the amplification loop, and subsequent generation of the membrane attack complex downstream; however, it has no effect on the initial activation mediated by the classical and lectin complement pathways. Therefore, Factor B is an attractive target for diseases in which the AP is overactivated. In this review, we provide an overview of Factor B and its critical role in the AP, discuss the benefit-risk of Factor B inhibition as a targeted therapeutic strategy, and describe the various Factor B inhibitors that are approved and/or in clinical development.

Induction of Fc-dependent functional antibodies against different variants of SARS-CoV-2 varies by vaccine type and prior infection

BACKGROUND

SARS-CoV-2 transmission and COVID-19 disease severity is influenced by immunity from natural infection and/or vaccination. Population-level immunity is complicated by the emergence of viral variants. Antibody Fc-dependent effector functions are as important mediators in immunity. However, their induction in populations with diverse infection and/or vaccination histories and against variants remains poorly defined.

METHODS

We evaluated Fc-dependent functional antibodies following vaccination with two widely used vaccines, AstraZeneca (AZ) and Sinovac (SV), including antibody binding of Fcγ-receptors and complement-fixation in vaccinated Brazilian adults (n = 222), some of who were previously infected with SARS-CoV-2, as well as adults with natural infection only (n = 200). IgG, IgM, IgA, and IgG subclasses were also quantified.

RESULTS

AZ induces greater Fcγ-receptor-binding (types I, IIa, and IIIa/b) antibodies than SV or natural infection. Previously infected individuals have significantly greater vaccine-induced responses compared to naïve counterparts. Fcγ-receptor-binding is highest among AZ vaccinated individuals with a prior infection, for all receptor types, and substantial complement-fixing activity is only seen among this group. SV induces higher IgM than AZ, but this does not drive better complement-fixing activity. Some SV responses are associated with subject age, whereas AZ responses are not. Importantly, functional antibody responses are well retained against the Omicron BA.1 S protein, being best retained for Fcγ-receptor-1 binding, and are higher for AZ than SV.

CONCLUSIONS

Hybrid immunity, from combined natural exposure and vaccination, generates strong Fc-mediated antibody functions which may contribute to immunity against evolving SARS-CoV-2 variants. Understanding determinants of Fc-mediated functions may enable future vaccines with greater efficacy against different variants.

The complement system: A key player in the host response to infections

Infections are one of the most significant healthcare and economic burdens across the world as underscored by the recent coronavirus pandemic. Moreover, with the increasing incidence of antimicrobial resistance, there is an urgent need to better understand host-pathogen interactions to design effective treatment strategies. The complement system is a key arsenal of the host defense response to pathogens and bridges both innate and adaptive immunity. However, in the contest between pathogens and host defense mechanisms, the host is not always victorious. Pathogens have evolved several approaches, including co-opting the host complement regulators to evade complement-mediated killing. Furthermore, deficiencies in the complement proteins, both genetic and therapeutic, can lead to an inefficient complement-mediated pathogen eradication, rendering the host more susceptible to certain infections. On the other hand, overwhelming infection can provoke fulminant complement activation with uncontrolled inflammation and potentially fatal tissue and organ damage. This review presents an overview of critical aspects of the complement-pathogen interactions during infection and discusses perspectives on designing therapies to mitigate complement dysfunction and limit tissue injury.

Complement and COVID-19: Three years on, what we know, what we don't know, and what we ought to know

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus was identified in China in 2019 as the causative agent of COVID-19, and quickly spread throughout the world, causing over 7 million deaths, of which 2 million occurred prior to the introduction of the first vaccine. In the following discussion, while recognising that complement is just one of many players in COVID-19, we focus on the relationship between complement and COVID-19 disease, with limited digression into directly-related areas such as the relationship between complement, kinin release, and coagulation. Prior to the 2019 COVID-19 outbreak, an important role for complement in coronavirus diseases had been established. Subsequently, multiple investigations of patients with COVID-19 confirmed that complement dysregulation is likely to be a major driver of disease pathology, in some, if not all, patients. These data fuelled evaluation of many complement-directed therapeutic agents in small patient cohorts, with claims of significant beneficial effect. As yet, these early results have not been reflected in larger clinical trials, posing questions such as who to treat, appropriate time to treat, duration of treatment, and optimal target for treatment. While significant control of the pandemic has been achieved through a global scientific and medical effort to comprehend the etiology of the disease, through extensive SARS-CoV-2 testing and quarantine measures, through vaccine development, and through improved therapy, possibly aided by attenuation of the dominant strains, it is not yet over. In this review, we summarise complement-relevant literature, emphasise its main conclusions, and formulate a hypothesis for complement involvement in COVID-19. Based on this we make suggestions as to how any future outbreak might be better managed in order to minimise impact on patients.

COVID-19: critical case of a patient with an atypical manifestation of the disease

BACKGROUND

COVID-19 was initially described as a severe acute respiratory disease that could drive to pneumonia, compromising the life of the patients in the worst scenario. However, even though in most of the cases the respiratory symptoms are still the most common manifestations of the disease, nowadays it is considered as a complex multisystem illness, affecting a variety of organs and tissues. Asymptomatic and atypic cases have also been described, where symptoms are not related to those first described, as is the case of this report.

CASE PRESENTATION

On November 23, 2020, a 53-year-old woman goes to the emergency room due to gastrointestinal symptoms. The admission diagnosis was inflammatory bowel disease and a mild event of idiopathic chronic ulcerative colitis, and the initial treatment was focused on the metabolic acidosis, and the reestablishment the hydroelectrolytic and hemodynamic balance. Then, she was transferred to the Gastroenterology Unit where she was treated for one week. During her hospitalization, she showed a refractory shock caused by progressive organ deterioration (renal and neurological), requiring a double-vasopressor support, oxygenation, and ventilation. Considering the laboratory tests results and computed tomography scans, a COVID-19 test was carried out, obtaining a positive result with a high viral load. The S gene of the virus was amplified and sequenced, finding an uncommon mutation rarely reported worldwide. After considerable systemic deterioration, the patient presented cardiorespiratory arrest, with no response and died on December 1, after 8 days of hospitalization.

CONCLUSIONS

In this report we describe the pathogenesis, clinical manifestations, and outcome of a patient with atypical COVID-19 symptoms (mainly gastrointestinal), rapidly evolving and with lethal consequences. Therefore, it is important to emphasize the need to strengthen patient surveillance in health centers, including those who do not present typical symptoms of COVID-19. In addition, it will be important to track the identified mutation (H1058Y) in the S viral gene and assess whether it could be associated with a different clinical manifestation of the disease or if it was just an isolated event.

Complement activation in COVID-19 and targeted therapeutic options: A scoping review

Increasing evidence suggests that activation of the complement system plays a key role in the pathogenesis and disease severity of Coronavirus disease 2019 (COVID-19). We used a systematic approach to create an overview of complement activation in COVID-19 based on histopathological, preclinical, multiomics, observational and clinical interventional studies. A total of 1801 articles from PubMed, EMBASE and Cochrane was screened of which 157 articles were included in this scoping review. Histopathological, preclinical, multiomics and observational studies showed apparent complement activation through all three complement pathways and a correlation with disease severity and mortality. The complement system was targeted at different levels in COVID-19, of which C5 and C5a inhibition seem most promising. Adequately powered, double blind RCTs are necessary in order to further investigate the effect of targeting the complement system in COVID-19.

Anti-C5a antibody (vilobelimab) therapy for critically ill, invasively mechanically ventilated patients with COVID-19 (PANAMO): a multicentre, double-blind, randomised, placebo-controlled, phase 3 trial

BACKGROUND

Vilobelimab, an anti-C5a monoclonal antibody, was shown to be safe in a phase 2 trial of invasively mechanically ventilated patients with COVID-19. Here, we aimed to determine whether vilobelimab in addition to standard of care improves survival outcomes in this patient population.

METHODS

This randomised, double-blind, placebo-controlled, multicentre phase 3 trial was performed at 46 hospitals in the Netherlands, Germany, France, Belgium, Russia, Brazil, Peru, Mexico, and South Africa. Participants aged 18 years or older who were receiving invasive mechanical ventilation, but not more than 48 h after intubation at time of first infusion, had a PaO2/FiO2 ratio of 60-200 mm Hg, and a confirmed SARS-CoV-2 infection with any variant in the past 14 days were eligible for this study. Eligible patients were randomly assigned (1:1) to receive standard of care and vilobelimab at a dose of 800 mg intravenously for a maximum of six doses (days 1, 2, 4, 8, 15, and 22) or standard of care and a matching placebo using permuted block randomisation. Treatment was not continued after hospital discharge. Participants, caregivers, and assessors were masked to group assignment. The primary outcome was defined as all-cause mortality at 28 days in the full analysis set (defined as all randomly assigned participants regardless of whether a patient started treatment, excluding patients randomly assigned in error) and measured using Kaplan-Meier analysis. Safety analyses included all patients who had received at least one infusion of either vilobelimab or placebo. This study is registered with ClinicalTrials.gov, NCT04333420.

FINDINGS

From Oct 1, 2020, to Oct 4, 2021, we included 368 patients in the ITT analysis (full analysis set; 177 in the vilobelimab group and 191 in the placebo group). One patient in the vilobelimab group was excluded from the primary analysis due to random assignment in error without treatment. At least one dose of study treatment was given to 364 (99%) patients (safety analysis set). 54 patients (31%) of 177 in the vilobelimab group and 77 patients (40%) of 191 in the placebo group died in the first 28 days. The all-cause mortality rate at 28 days was 32% (95% CI 25-39) in the vilobelimab group and 42% (35-49) in the placebo group (hazard ratio 0·73, 95% CI 0·50-1·06; p=0·094). In the predefined analysis without site-stratification, vilobelimab significantly reduced all-cause mortality at 28 days (HR 0·67, 95% CI 0·48-0·96; p=0·027). The most common TEAEs were acute kidney injury (35 [20%] of 175 in the vilobelimab group vs 40 [21%] of 189 in the placebo), pneumonia (38 [22%] vs 26 [14%]), and septic shock (24 [14%] vs 31 [16%]). Serious treatment-emergent adverse events were reported in 103 (59%) of 175 patients in the vilobelimab group versus 120 (63%) of 189 in the placebo group.

INTERPRETATION

In addition to standard of care, vilobelimab improves survival of invasive mechanically ventilated patients with COVID-19 and leads to a significant decrease in mortality. Vilobelimab could be considered as an additional therapy for patients in this setting and further research is needed on the role of vilobelimab and C5a in other acute respiratory distress syndrome-causing viral infections.

FUNDING

InflaRx and the German Federal Government.

Update on Innate Immunity in Acute Kidney Injury—Lessons Taken from COVID-19

The serious clinical course of SARS-CoV-2 infection is usually accompanied by acute kidney injury (AKI), worsening prognosis and increasing mortality. AKI in COVID-19 is above all a consequence of systemic dysregulations leading to inflammation, thrombosis, vascular endothelial damage and necrosis. All these processes rely on the interactions between innate immunity elements, including circulating blood cells, resident renal cells, their cytokine products, complement systems, coagulation cascades and contact systems. Numerous simultaneous pathways of innate immunity should secure an effective host defense. Since they all form a network of cross-linked auto-amplification loops, uncontrolled activation is possible. When the actions of selected pathways amplify, cascade activation evades control and the propagation of inflammation and necrosis worsens, accompanied by complement overactivity and immunothrombosis. The systemic activation of innate immunity reaches the kidney, where the damage affecting single tubular cells spreads through tissue collateral damage and triggers AKI. This review is an attempt to synthetize the connections between innate immunity components engaged in COVID-19-related AKI and to summarize the knowledge on the pathophysiological background of processes responsible for renal damage.

C3a and C5b-9 Differentially Predict COVID-19 Progression and Outcome

SARS-CoV-2 infection may result in severe pneumonia leading to mechanical ventilation and intensive care (ICU) treatment. Complement activation was verified in COVID-19 and implicated as a contributor to COVID-19 pathogenesis. This study assessed the predictive potential of complement factors C3a and C5b-9 for COVID-19 progression and outcome. We grouped 80 COVID-19 patients into severe COVID-19 patients (n = 38) and critically ill (n = 42) and subdivided into non-intubated (n = 48) and intubated (n = 32), survivors (n = 57) and non-survivors (n = 23). Results: A significant increase for C3a and C5b-9 levels was observed between: severely and critically ill patients (p < 0.001 and p < 0.0001), non-intubated vs intubated (p < 0.001 and p < 0.05), survivors vs non-survivors (p < 0.001 and p < 0.01). ROC analysis for the need for ICU treatment revealed a higher AUC for C5b-9 (0.764, p < 0.001) compared to C3a (AUC = 0.739, p < 0.01). A higher AUC was observed for C3a for the need for intubation (AUC = 0.722, p < 0.001) or mortality (AUC = 0.740, p < 0.0001) compared to C5b-9 (need for intubation AUC = 0.656, p < 0.05 and mortality AUC = 0.631, p = NS). Combining the two markers revealed a powerful prediction tool for ICU admission (AUC = 0.773, p < 0.0001), intubation (AUC = 0.756, p < 0.0001) and mortality (AUC = 0.753, p < 0.001). C3a and C5b-9 may be considered as prognostic tools separately or in combination for the progression and outcome of COVID-19.

C5a elevation in convalescents from severe COVID-19 is not associated with early complement activation markers C3bBbP or C4d

Numerous publications have underlined the link between complement C5a and the clinical course of COVID-19. We previously reported that levels of C5a remain high in the group of severely ill patients up to 90 days after hospital discharge. We have now evaluated which complement pathway fuels the elevated levels of C5a during hospitalization and follow-up. The alternative pathway (AP) activation marker C3bBbP and the soluble fraction of C4d, a footprint of the classical/lectin (CP/LP) pathway, were assessed by immunoenzymatic assay in a total of 188 serial samples from 49 patients infected with SARS-CoV-2. Unlike C5a, neither C3bBbP nor C4d readouts rose proportionally to the severity of the disease. Detailed correlation analyses in hospitalization and follow-up samples collected from patients of different disease severity showed significant positive correlations of AP and CP/LP markers with C5a in certain groups, except for the follow-up samples of the patients who suffered from highly severe COVID-19 and presented the highest C5a readouts. In conclusion, there is not a clear link between persistently high levels of C5a after hospital discharge and markers of upstream complement activation, suggesting the existence of a non-canonical source of C5a in patients with a severe course of COVID-19.

Duration of COVID-19 mRNA Vaccine Effectiveness against Severe Disease

Waning immunity following administration of mRNA-based COVID-19 vaccines remains a concern for many health systems. We undertook a study to determine if recent reports of waning for severe disease could have been attributed to design-related bias by conducting a study only among those detected with a first SARS-CoV-2 infection. We used a matched case-control study design with the study base being all individuals with first infection with SARS-CoV-2 reported in the State of Qatar between 1 January 2021 and 20 February 2022. Cases were those detected with first SARS-CoV-2 infection requiring intensive care (hard outcome), while controls were those detected with first SARS-CoV-2 infection who recovered without the need for intensive care. Cases and controls were matched in a 1:30 ratio for the calendar month of infection and the comorbidity category. Duration and magnitude of conditional vaccine effectiveness against requiring intensive care and the number needed to vaccinate (NNV) to prevent one more case of COVID-19 requiring intensive care was estimated for the mRNA (BNT162b2/mRNA-1273) vaccines. Conditional vaccine effectiveness against requiring intensive care was 59% (95% confidence interval (CI), 50 to 76) between the first and second dose, and strengthened to 89% (95% CI, 85 to 92) between the second dose and 4 months post the second dose in persons who received a primary course of the vaccine. There was no waning of vaccine effectiveness in the period from 4 to 6, 6 to 9, and 9 to 12 months after the second dose. This study demonstrates that, contrary to mainstream reports using hierarchical measures of effectiveness, conditional vaccine effectiveness against requiring intensive care remains robust till at least 12 months after the second dose of mRNA-based vaccines.

Sex-adjusted approach to baseline variables demonstrated some improved predictive capabilities for disease severity and survival in patients with Coronavirus Disease 19

INTRODUCTION

The study was focused on comparing crude and sex-adjusted hazard ratio calculated by the baseline variables which may have contributed to the severity of the disease course and fatal outcomes in Coronavirus Disease-19 (COVID-19) patients.

METHOD

The study enrolled 150 eligible adult patients with confirmed SARS-CoV-2 infection. There were 61 (40.7%) male patients, and 89 (59.3%) female patients. Baseline information of patients was collected from patient medical records and surveys that the patients had completed on admission to the hospital.

RESULTS

Considerable number of baseline variables stratified according to disease severity and outcomes showed different optimal cut-points (OCP) in men and women. Sex-adjusted baseline data categories such as age; BMI; systolic and diastolic blood pressure; peripheral RBC and platelet counts; haematocrit; percentage of neutrophils, lymphocytes, monocytes, and their ratio; percentage of eosinophils; titre of plasma IL-6, IL-8, IL-10, and IL-17; and CXCL10; and ratio of pro- and anti-inflammatory cytokines demonstrated significant impacts on the development of the severe stage and fatal outcomes by the mean hazard ratio in the Kaplan-Meier and Cox regression models.

CONCLUSION

This study confirmed some improved predictive capabilities of the sex-adjusted approach in the analysis of the baseline predictive variables for severity and outcome of the COVID-19.

α2,6-Sialylation is Upregulated in Severe COVID-19 Implicating the Complement Cascade

Better understanding of the mechanisms of COVID-19 severity is desperately needed in current times. Although hyper-inflammation drives severe COVID-19, precise mechanisms triggering this cascade and what role glycosylation might play therein is unknown. Here we report the first high-throughput glycomic analysis of COVID-19 plasma samples and autopsy tissues. We find α2,6-sialylation is upregulated in plasma of patients with severe COVID-19 and in the lung. This glycan motif is enriched on members of the complement cascade, which show higher levels of sialylation in severe COVID-19. In the lung tissue, we observe increased complement deposition, associated with elevated α2,6-sialylation levels, corresponding to elevated markers of poor prognosis (IL-6) and fibrotic response. We also observe upregulation of the α2,6-sialylation enzyme ST6GAL1 in patients who succumbed to COVID-19. Our work identifies a heretofore undescribed relationship between sialylation and complement in severe COVID-19, potentially informing future therapeutic development.

SARS-CoV-2 Induces Cytokine Responses in Human Basophils

Basophils play a key role in the orientation of immune responses. Though the interaction of SARS-CoV-2 with various immune cells has been relatively well studied, the response of basophils to this pandemic virus is not characterized yet. In this study, we report that SARS-CoV-2 induces cytokine responses and in particular IL-13, in both resting and IL-3 primed basophils. The response was prominent under IL-3 primed condition. However, either SARS-CoV-2 or SARS-CoV-2-infected epithelial cells did not alter the expression of surface markers associated with the activation of basophils, such as CD69, CD13 and/or degranulation marker CD107a. We also validate that human basophils are not permissive to SARS-CoV-2 replication. Though increased expression of immune checkpoint molecule PD-L1 has been reported on the basophils from COVID-19 patients, we observed that SARS-CoV-2 does not induce PD-L1 on the basophils. Our data suggest that basophil cytokine responses to SARS-CoV-2 might help in reducing the inflammation and also to promote antibody responses to the virus.