Clinical bottom line
Emerging therapies targeting complement system dysregulation represent a promising frontier in the management of autoimmune diseases characterized by aberrant complement activation, such as certain kidney disorders and systemic autoimmune conditions. Early-phase clinical and mechanistic studies suggest these agents may improve disease control by modulating complement pathways implicated in tissue injury and immune dysregulation. However, current evidence remains preliminary, with limited large-scale randomized controlled trials and incomplete long-term safety data. Clinicians should consider complement-targeted therapies as potential adjuncts in refractory or severe cases while awaiting further validation.
What the evidence shows
Complement system dysregulation contributes to the pathogenesis of multiple autoimmune diseases by promoting inflammation, tissue damage, and immune complex deposition. Recent advances have identified key complement components and pathways amenable to pharmacologic intervention. Jesiołowski et al. (2026) provide a comprehensive review of complement dysregulation in kidney diseases, highlighting mechanisms such as alternative pathway overactivation and the role of complement split products as biomarkers. They also discuss emerging targeted therapies including C3 and C5 inhibitors, which have shown efficacy in reducing complement-mediated renal injury in early clinical studies.
Beyond nephrology, complement-targeting agents are under investigation for systemic autoimmune diseases where complement activation exacerbates pathology. Chatenoud et al. (2020) emphasize the expanding landscape of biological and molecular therapies, noting complement inhibitors as a novel class with potential to modulate immune responses more precisely than broad immunosuppression. These therapies may offer improved specificity and reduced off-target effects compared to conventional treatments.
While the field is evolving, clinical data remain limited. Most evidence derives from phase 1/2 trials or observational cohorts, often focusing on rare complement-mediated conditions. Safety profiles appear acceptable in short-term use, but long-term risks such as infection susceptibility require careful monitoring. The heterogeneity of autoimmune diseases and complement involvement necessitates biomarker-driven patient selection to optimize therapeutic benefit.
Caveats and uncertainty
The current evidence base is largely hypothesis-generating and derived from small, early-phase studies. Many complement inhibitors are still in clinical development or approved only for specific indications (e.g., paroxysmal nocturnal hemoglobinuria), limiting generalizability. The complexity of complement biology and redundancy in pathways may attenuate efficacy or lead to compensatory mechanisms.
Additionally, the identification of reliable biomarkers to stratify patients who will benefit most from complement inhibition remains an unmet need. Jesiołowski et al. (2026) underscore that complement activity assays and genetic profiling are not yet standardized for routine clinical use. Safety concerns, particularly regarding infection risk due to impaired opsonization, require vigilance and possibly prophylactic strategies.
Finally, cost and accessibility of complement-targeted therapies may pose barriers to widespread adoption. Longitudinal studies are needed to assess sustained efficacy, optimal dosing, and integration with existing immunomodulatory regimens.
How this may change practice
As evidence matures, complement system modulation could become an integral component of personalized autoimmune disease management, especially for patients with refractory disease or those exhibiting complement-driven pathology. Clinicians should remain informed about ongoing clinical trials and emerging guidelines to identify candidates for such therapies.
Incorporation of complement biomarkers into diagnostic and monitoring algorithms may facilitate earlier intervention and treatment tailoring. Complement inhibitors might reduce reliance on broad immunosuppression, potentially lowering adverse event rates.
Until robust phase 3 data are available, complement-targeted therapies should be considered experimental outside approved indications. Multidisciplinary collaboration with nephrologists, rheumatologists, and immunologists will be essential to optimize patient outcomes and safety.