Complement C3 vs C5 inhibition in severe COVID-19: early clinical findings reveal differential biological efficacy

Growing clinical evidence has implicated complement as a pivotal driver of COVID-19 immunopathology. Deregulated complement activation may fuel cytokine-driven hyper-inflammation, thrombotic microangiopathy and NET-driven immunothrombosis, thereby leading to multi-organ failure. Complement therapeutics have gained traction as candidate drugs for countering the detrimental consequences of SARS-CoV-2 infection. Whether blockade of terminal complement effectors (C5, C5a, or C5aR1) can elicit similar outcomes to upstream intervention at the level of C3 remains debated. Here we have compared the clinical efficacy of the C5-targeting mAb eculizumab with that of the compstatin-based C3-targeted drug candidate AMY-101 in small independent cohorts of severe, mainly non-intubated COVID-19 patients. Our exploratory study indicates that therapeutic complement inhibition abrogates COVID-19 hyper-inflammation. Both C3 and C5 inhibitors elicit a robust anti-inflammatory response, reflected by a steep decline in CRP and IL-6 levels, associated with marked lung function improvement and resolution of SARS-CoV-2-associated ARDS. C3 inhibition afforded broader therapeutic control in COVID19 patients by attenuating both C3a and sC5b-9 generation and preventing FB consumption. This broader inhibitory profile of anti-C3 treatment was associated with a more robust decline of neutrophil counts, a greater decline of median LDH levels and more prominent lymphocyte recovery within the first 7 days of treatment. These early clinical results offer important insight into the differential mechanistic basis and underlying biology of C3 and C5 inhibition in COVID-19. They point to a broader pathogenic involvement of C3-mediated pathways and set the stage for larger prospective trials that will benchmark these complement-targeting agents in COVID-19.

Complement and tissue factor-enriched neutrophil extracellular traps are key drivers in COVID-19 immunothrombosis

Emerging data indicate that complement and neutrophils are involved in the maladaptive host immune response that fuels hyper-inflammation and thrombotic microangiopathy increasing the mortality rate in coronavirus disease 2019 (COVID-19). Here, we investigated the interaction between complement and the platelet/neutrophil extracellular traps (NETs)/thrombin axis, using COVID-19 clinical samples, cell-based inhibition studies and NETs/human aortic endothelial cell (HAEC) co-cultures. Increased plasma levels of NETs, TF activity and sC5b-9 were detected in patients. Neutrophils yielded high tissue factor (TF) expression and released NETs carrying functionally active TF. Confirming our ex vivo findings, treatment of control neutrophils with COVID-19 platelet-rich plasma generated TF-bearing NETs that induced thrombotic activity of HAEC. Thrombin or NETosis inhibition or C5aR1 blockade attenuated platelet-mediated NET-driven thrombogenicity. Serum isolated from COVID-19 patients induces complement activation in vitro, which is consistent with high complement activity in clinical samples. Complement inhibition at the level of C3 with compstatin Cp40 disrupted TF expression in neutrophils. In conclusion, we provide a mechanistic basis that reveals the pivotal role of complement and NETs in COVID-19 immmunothrombosis. This study supports emerging strategies against SARS-CoV-2 infection that exploit complement therapeutics or NETosis inhibition.

Erythrocytes Reveal Complement Activation in Patients with COVID-19

COVID-19, the disease caused by the SARS-CoV-2 virus, can progress to multi-organ failure characterized by respiratory insufficiency, arrhythmias, thromboembolic complications and shock 1-5. The mortality of patients hospitalized with COVID-19 is unacceptably high and new strategies are urgently needed to rapidly identify and treat patients at risk for organ failure. Clinical epidemiologic studies demonstrate that vulnerability to organ failure is greatest after viral clearance from the upper airway 6-8, which suggests that dysregulation of the host immune response is a critical mediator of clinical deterioration and death. Autopsy and pre-clinical evidence implicate aberrant complement activation in endothelial injury and organ failure 9,10. A potential therapeutic strategy warranting investigation is to inhibit complement, with case reports of successful treatment of COVID-19 with inhibitors of complement 10-13. However, this approach requires careful balance between the host protective and potential injurious effects of complement activation, and biomarkers to identify the optimal timing and candidates for therapy are lacking. Here we report the presence of complement activation products on circulating erythrocytes from hospitalized COVID-19 patients using flow cytometry. These findings suggest that novel erythrocyte-based diagnostics provide a method to identify patients with dysregulated complement activation.