Complement System Therapeutics for Neurodegeneration

Latest Data Snapshot (March 2026)

> Data refreshed: 2026-03-14 PT from ClinicalTrials.gov

| Metric | Value |
|---|---:|
| Total Clinical Trials | 28 |
| Active Trials (Recruiting/Active) | 8 (29%) |
| Phase 1 Trials | 5 |
| Phase 2 Trials | 3 |
| Phase 3 Trials | 0 |

Overview

Latest Data Snapshot (March 2026)

> Data refreshed: 2026-03-14 PT from ClinicalTrials.gov

| Metric | Value |
|---|---:|
| Total Clinical Trials | 28 |
| Active Trials (Recruiting/Active) | 8 (29%) |
| Phase 1 Trials | 5 |
| Phase 2 Trials | 3 |
| Phase 3 Trials | 0 |

Overview

The [complement system](/entities/complement-system) is a critical component of the innate immune system that plays a dual role in neurodegeneration - both in protective immune surveillance and in driving pathological neuroinflammation. Therapeutic targeting of complement proteins represents a growing area of interest for Alzheimer's disease, Parkinson's disease, and other neurodegenerative disorders["@complement2022"].

The complement system has emerged as a key link between neuroinflammation and protein aggregation in neurodegenerative diseases. While complement proteins play essential roles in synaptic pruning during development and immune defense, dysregulated complement activation can drive pathology through microglial activation, synapse loss, and chronic neuroinflammation.

Investment Context

The complement therapeutics space has seen significant investment following:

• Success in other indications: C5 inhibitors (eculizumab, ravulizumab) are approved for rare diseases
• Alzheimer's genetics: [TREM2](/proteins/trem2) variants highlight microglial pathways linked to complement
• Anti-CD20 de-risking: Similar immune modulation approach validated in MS

• [BBB](/entities/blood-brain-barrier) penetration: Most complement inhibitors are large biologics
• Infection risk: Complement inhibition increases susceptibility to infections
• Timing: Optimal patient selection (early vs. late disease) unclear

Key Complement Targets

| Target | Role in Neurodegeneration | Therapeutic Approach | Development Stage |
|--------|-------------------------|---------------------|-------------------|
| C1q | Synaptic pruning, complement activation | Antibody blockade | Preclinical |
| C3 | Central complement node | C3 inhibitor (Pegcetacoplan) | Phase 2 |
| C5 | Complement terminal pathway | Eculizumab, Ravulizumab | Approved (other), Phase 2/3 |
| C5aR1 | Neuroinflammation receptor | C5a receptor antagonists | Preclinical |
| C1QA | Synaptic elimination | Genetic studies | Research |

Clinical Pipeline

C3 Inhibitors

• Pegcetacoplan (Apellis): intravitreal formulation approved for geographic atrophy; systemic formulation in trials for AD[@pegcetacoplan]

C5 Inhibitors

• Eculizumab (Alexion): Approved for PNH and aHUS; being explored for ALS
• Ravulizumab (Alexion): Long-acting C5 inhibitor; Phase 2 trials in ALS

Emerging Programs

• Nodthera: [NLRP3 inflammasome](/entities/nlrp3-inflammasome) + complement dual approach
• Roche: Anti-C1q antibodies in development for CNS indications

Companies Active in Complement

• Alexion (AstraZeneca): C5 inhibitors (eculizumab, ravulizumab)
• Apellis Pharmaceuticals: C3 inhibitor (pegcetacoplan)
• Roche/Genentech: Anti-C1q program
• NodThera: NLRP3/complement dual inhibitors

Gap Analysis

Underrepresented Areas

Opportunities

• Genetic validation from AD genetics (C1QA, C1QB variants)
• Link to TREM2 pathway provides biological rationale
• Synaptic protection as potential disease-modifying mechanism

Conclusion

Complement therapeutics represent a promising but challenging area in neurodegeneration R&D. While the biological rationale is strong, BBB penetration and infection risk remain key hurdles. The field awaits late-stage clinical data to validate this approach.

Cross-Links

• [C1Q](/genes/c1qa)
• [C3](/genes/c3)
• [C5](/genes/c5)
• [C5A1R](/genes/c5ar1)
• [TREM2](/genes/trem2)
• [Neuroinflammation](/mechanisms/neuroinflammation)
• [Microglia](/cell-types/microglia)

See Also

• [Novel Therapy Index](/ideas/novel-therapy-index)
• [Investment Landscape: Neuroinflammation](/content/investment)
• [Investment Landscape: TREM2](/content/investment)

• [Complement System](/entities/complement-system)
• Complement Inhibition

• [Complement in Neurodegeneration](https://www.frontiersin.org/articles/10.3389/fnins.2020.576527/full)

References