One pathway, two organs: the shared pathology of GA and C3G

Geographic atrophy (GA) and C3 glomerulopathy (C3G) are driven by the same molecular defect — hyperactivation of the complement alternative pathway (CAP) — even though the tissue destruction unfolds in entirely different organs. In GA, uncontrolled C3 cleavage and downstream membrane attack complex (MAC, C5b-9) formation drives progressive retinal pigment epithelium (RPE) degeneration in the absence of any approved therapy for non-exudative AMD. In C3G, the same complement dysregulation causes C3d deposition in the renal glomerulus, leading to a rare and refractory kidney disease with a prevalence estimated at approximately 2–3 per million people.

The structural parallel between the two diseases extends beyond pathway biology. Retrieved patent filings from Ionis Pharmaceuticals explicitly note the shared developmental biology between the kidney and eye — both sharing type IV collagen basement membrane composition and vascular architecture — as a biological rationale for a single Complement Factor B (CFB)-targeting agent to address pathology across both organs. This cross-organ rationale underpins the broadest commercial IP strategies in this space, where a single compound can be positioned across GA, C3 glomerulonephritis (C3GN), dense deposit disease (DDD), and atypical hemolytic uremic syndrome (aHUS).

The central molecular node across both diseases is Complement Factor B, the rate-limiting serine protease of the CAP C3 convertase (C3bBb). Inhibiting CFB prevents assembly of the C3 amplification loop and reduces both C3b glomerular deposition relevant to C3G and subretinal C3 accumulation relevant to GA. This mechanistic centrality explains why CFB has attracted the densest cluster of patent filings in this dataset, with Ionis Pharmaceuticals prosecuting an ASO franchise across eight jurisdictions simultaneously. As documented by WIPO, the breadth of jurisdictional coverage is a reliable indicator of commercial prosecution intent in pharmaceutical IP.

Complement Factor B: the dominant commercial IP target

Complement Factor B is the most densely covered target in this patent dataset, with Ionis Pharmaceuticals holding the most prolific and geographically extensive portfolio. The company’s antisense oligonucleotide (ASO) program — centred on Compound 696844 (also designated ISIS 696844) — claims CFB inhibition via RNase H-mediated degradation of CFB mRNA, reducing C3 convertase assembly and downstream complement amplification. Filings span WO, SG, IL, CA, AU, MX, CN, and JP jurisdictions, with active prosecution as recently as 2024–2025.

“Complement Factor B is the rate-limiting serine protease of the CAP C3 convertase. Ionis Pharmaceuticals prosecutes its CFB ASO franchise across eight jurisdictions simultaneously — the broadest single-target complement IP footprint in this dataset.”

Beyond Ionis, the CFB target space is reinforced by Complement Factor I (CFI) as a closely related alternative. Retrieved gene therapy filings from The Sydney Children’s Hospitals Network and Gyroscope Therapeutics describe CFI as a superior target to Factor H, citing CFI’s lower physiological serum concentration — approximately 35 µg/mL versus 200–500 µg/mL for Factor H — as enabling smaller therapeutic doses. CFI also lacks the competitive interference from Factor H-related proteins (FHR1–5) and performs a unique enzymatic step: the conversion of iC3b to C3dg, which is critical for resolving complement-mediated inflammation rather than merely slowing it.

Drug developers and IP strategists assessing freedom-to-operate in the complement space should treat CFB as a heavily encumbered target. The Ionis ASO franchise — particularly sequences overlapping Compound 696844/ISIS 696844 — represents a potential blocking position across both GA and multiple renal indications. According to the European Patent Office, antisense oligonucleotide patents with sequence-specific claims can create narrow but enforceable exclusivity zones that require careful sequence differentiation strategies from competing programs.

Mapping the therapeutic modalities across the complement cascade

The complement-targeting therapy landscape in GA and C3G is not a single-modality field — it is a multi-level intervention map spanning every major node of the complement alternative pathway, from upstream C3 suppression to terminal C5a receptor blockade. Retrieved patent filings identify at least ten distinct mechanistic approaches, each with a different assignee, target, and clinical rationale.

Upstream suppression: C3-directed modalities

Three mechanistically distinct approaches target C3 directly. AstraZeneca (Ireland) filed a Chinese patent covering RNAi oligonucleotides targeting C3 mRNA across the broadest disease spectrum in this dataset — including C3G, DDD, AMD/GA, IgA nephropathy, lupus nephritis, and FSGS. Catalyst Biosciences and Vertex Pharmaceuticals hold patents on modified urokinase-type plasminogen activator (u-PA) polypeptides engineered to cleave complement protein C3, representing an enzymatic cleavage approach distinct from antibody or oligonucleotide modalities. Potentia Pharmaceuticals’ compstatin patent covers C3 inhibition through direct peptide binding, preventing C3 cleavage and all downstream amplification, specifically for AMD and macular degeneration.

Terminal pathway and receptor-level blockade

ChemoCentRyx’s C5aR antagonist program — centred on avacopan — is the most C3G-specific approach in this dataset. The mechanism involves blockade of the C5a receptor (C5aR1), preventing downstream inflammatory signalling without blocking MAC formation. This is a deliberate distinction from upstream C3 or C5 inhibition, which carries systemic immunosuppression risk. Kira Pharmaceuticals adds a dual-mechanism layer with a fusion protein comprising an anti-C5 antibody moiety fused to Factor H, explicitly claiming C3G and IgA nephropathy alongside paroxysmal nocturnal hemoglobinuria (PNH) and SLE-associated thrombotic microangiopathy.

Soluble CR1 and fusion proteins for kidney-targeted delivery

Soluble complement receptor type 1 (sCR1), disclosed in patents from Zhang Yuzhou and the University of Iowa Research Foundation, functions as a fluid-phase and surface complement regulatory protein blocking both C3 and C5 convertases of the alternative pathway. The WO filing explicitly acknowledges that addressing continuous alternative pathway activation as a viable therapy was previously uncertain, positioning sCR1 as a proof-of-concept modality for DDD, C3G, and aHUS. Q32 Bio and Alexion Pharmaceuticals are developing fusion proteins that actively target the kidney — via VHH, integrin-binding, or antigen-specific antibody domains — while delivering complement regulators (Factor H catalytic domains, CR1, DAF, CD59) locally, addressing the challenge of systemic complement suppression with organ-specific delivery.

Clinical signals, lampalizumab’s failure, and what came next

The most consequential clinical event shaping the current complement-targeting therapy landscape is the failure of lampalizumab — an anti-Factor D humanized monoclonal antibody administered by intravitreal injection — in the Phase III MAHALO study. The trial enrolled 906 participants and found that lampalizumab failed to reduce GA enlargement compared to sham over 48 weeks. Multiple retrieved patent filings from Gyroscope Therapeutics, The Sydney Children’s Hospitals Network, and others explicitly cite this failure as justification for their novel approaches, indicating that CFI gene therapy and CFB ASO programs were specifically designed in response to this clinical data.

The lampalizumab failure also surfaced a critical insight about patient population design. Factor D inhibition was applied to an undifferentiated GA population, without stratifying for complement pathway activity. The Oak Bay Biosciences WO patent filing directly addresses this gap, describing methods for stratifying GA patients into hyperactive, homeostatic, and hypoactive complement groups. The filing claims at least 40% enrichment in GA slowing for patients identified as having hyperactive complement pathway activity — language consistent with post-hoc analysis of clinical trial data or prospective clinical protocol design. According to published research accessible through the National Institutes of Health, biomarker-driven patient enrichment strategies have become standard practice in rare disease trials where undifferentiated populations dilute treatment effects.

The CFB ASO program from Ionis Pharmaceuticals shows multiple clinical-stage signals. Retrieved filings include dose-adjustment language — provisions for increasing or decreasing dose based on biomarker comparisons — and plasma/serum CFB level monitoring as pharmacokinetic readouts. Late-stage prosecution activity (AU 2025 pending, WO 2024 pending) across multiple jurisdictions is consistent with ongoing or completed clinical studies. Regeneron’s humanized C3 transgenic mouse model, disclosed in JP and WO patents, provides IND-enabling preclinical tooling for candidate screening in complement-associated nephropathy — explicitly described as applicable to aHUS, DDD, and C3GN — indicating active drug screening infrastructure at the preclinical stage.

Combination strategies and emerging precision approaches

Complement monotherapy is increasingly challenged by combination approaches that address multiple pathological drivers simultaneously. Retrieved patent filings signal at least four convergent combination strategies that are reshaping the competitive landscape across both GA and C3G.

Anti-VEGF plus complement inhibition for AMD/GA

Gyroscope Therapeutics’ Mexican patent (2023) explicitly covers combined nucleic acid products encoding an anti-VEGF entity — preferably aflibercept — and a negative complement regulator (CFI or FHL1) for AMD. Innovent Biologics discloses bispecific fusion proteins simultaneously inhibiting complement and VEGF pathways, noting that anti-complement drugs alone show unclear efficacy in wet AMD without anti-VEGF co-administration. A bifunctional fusion protein from Sanyu Biotech targeting both complement and VEGF via dual human protein domain constructs is also retrieved. These three patent families signal convergence toward dual-pathway inhibition for neovascular and atrophic AMD — a competitive threat to complement monotherapy programs in the AMD space. As documented in research published via Nature, dual-mechanism biologics in ophthalmology have demonstrated improved durability over single-pathway agents in neovascular disease.

Anti-C5 antibody plus C5 RNAi co-formulation

Regeneron’s Chinese patent filing for an anti-C5 antibody/C5 iRNA co-formulation with GalNAc conjugation seeks to achieve deeper, more sustained C5 suppression than monotherapy. The rationale is explicit in the filing: applications extend to complement-sensitive diseases where current C5 inhibitors are insufficient as single agents. This approach parallels the bispecific antibody strategy disclosed by Broadwing Bio (Japan patent, 2025), which targets two components of the complement alternative pathway activation system simultaneously for GA treatment — the most recent multi-target filing in this dataset.

Precision complement medicine: biomarker stratification as a companion diagnostic

The Oak Bay Biosciences patient stratification approach for GA — classifying patients by hyperactive, homeostatic, or hypoactive CAP activity — signals a shift toward precision complement medicine where treatment is contingent on biomarker-defined pathway hyperactivity. The claimed ≥40% enrichment in GA slowing for hyperactive patients is a substantial effect-size claim that, if validated, would make complement pathway activity testing a prerequisite for trial enrollment and potentially for commercial reimbursement. This paradigm is potentially applicable across both GA and C3G, given the shared pathophysiological driver.

“Oak Bay Biosciences claims at least 40% enrichment in GA slowing for patients stratified as having hyperactive complement pathway activity — a finding that could make biomarker testing a prerequisite for complement therapy reimbursement.”

For clinical and investment teams evaluating complement inhibitors for GA, the Oak Bay Biosciences stratification data — and the broader lesson of lampalizumab’s undifferentiated population failure — suggests that trial enrichment strategies based on CAP hyperactivity biomarkers may be necessary to demonstrate efficacy in pivotal trials. The FDA‘s increasing emphasis on companion diagnostics in rare disease drug approvals reinforces this direction. Developers pursuing complement monotherapy in AMD should also anticipate competitive pressure from bifunctional programs offering a single-administration dual benefit against both complement and VEGF pathways.