Novel Treatment Paradigms: Complement Inhibition in Antineutrophil Cytoplasmic Autoantibody Vasculitis

A growing body of evidence has highlighted the critical role of complement activation-particularly through the alternative pathway-in the pathogenesis of antineutrophil cytoplasmic autoantibody (ANCA) vasculitis. Foundational insights first emerged from landmark mouse model studies, which have been further substantiated by findings in human ANCA vasculitis. In addition, measuring complement activation fragments in circulation and urine may correlate with disease activity and may serve as sensitive biomarkers for disease monitoring. C5a and C5a receptor engagement has been shown to be particularly important for mediating disease and has been a central therapeutic target. Avacopan is an oral small molecule C5a receptor antagonist approved as adjunctive therapy to standard treatments for severe active ANCA vasculitis. Studies have shown that avacopan can reduce disease activity, proteinuria, and glucocorticoid exposure; and may even allow for greater kidney recovery in patients with ANCA vasculitis and severe renal insufficiency. Additional therapies targeting various components of the complement cascade are under investigation or in development, generating considerable excitement for novel treatment strategies in ANCA vasculitis. This review discusses key clinical developments and summarizes pivotal clinical trials evaluating complement inhibition in ANCA vasculitis. Although early results suggest that complement inhibitors may offer more effective and safer alternatives to established therapies, there are limitations and barriers that prevent their more widespread use. Further research is needed to better understand their efficacy and long-term safety and to inform how to optimize their integration into treatment paradigms for ANCA vasculitis.