argenx Unveils Positive Phase 2 Results for Efgartigimod in Myositis and Sjogren’s Disease at EULAR 2025
argenx SE a global immunology company dedicated to advancing treatments for severe autoimmune diseases, presented encouraging new clinical data at the 2025 European Congress of Rheumatology (EULAR), held June 11–14 in Barcelona, Spain. The data come from Phase 2 trials evaluating its investigational therapy VYVGART® (efgartigimod) for two hard-to-treat autoimmune conditions: idiopathic inflammatory myopathies (IIM or myositis) and Sjogren’s disease (SjD). These results support efgartigimod’s potential as a targeted therapeutic approach to conditions marked by pathogenic IgG autoantibodies.
Additionally, argenx announced that the U.S. Food and Drug Administration (FDA) has granted Fast Track Designation (FTD) to efgartigimod for the treatment of primary Sjogren’s disease, further accelerating its pathway toward potential regulatory approval.
Expanding the Role of Efgartigimod in Autoimmune Diseases
“Our innovation model prioritizes a strong biological rationale and agile clinical design, enabling us to efficiently move forward in rheumatologic diseases,” said Dr. Luc Truyen, Chief Medical Officer at argenx. “With a growing body of data confirming the role of IgG autoantibodies in disease pathology, we believe efgartigimod has the potential to become a precision therapy that targets the root cause, not just the symptoms. The results from our myositis and Sjogren’s programs presented at EULAR 2025 reflect this potential.”
Efgartigimod, an FcRn antagonist, works by reducing circulating IgG antibodies, which are known contributors to multiple autoimmune conditions. The company is pursuing both intravenous (IV: efgartigimod alfa-fcab) and subcutaneous (SC or Hytrulo: efgartigimod alfa and hyaluronidase-qvfc) formulations to optimize patient access and treatment flexibility.
Promising Results in Myositis: ALKIVIA Phase 2/3 Trial
The ALKIVIA study is a seamless Phase 2/3 trial evaluating efgartigimod in three key subtypes of myositis: immune-mediated necrotizing myopathy (IMNM), antisynthetase syndrome (ASyS), and dermatomyositis (DM). At EULAR 2025, argenx presented the results from the Phase 2 portion, demonstrating robust and statistically significant treatment benefits across multiple disease measures.
Key Efficacy Outcomes:
- Primary Endpoint Met: The primary endpoint was the mean Total Improvement Score (TIS) at 24 weeks, a composite measure incorporating six core indicators of disease activity and muscle function. Patients receiving efgartigimod achieved a mean TIS of 50.45, significantly higher than the placebo group’s 35.65 (p=0.0004).
- Meaningful Clinical Response Rates:
- 79% of patients in the efgartigimod group achieved a moderate improvement (TIS ≥40), compared to 47% in the placebo group.
- 34% achieved a major improvement (TIS ≥60), compared to just 9.5% in the placebo group.
Rapid Onset and Durable Effects:
- Patients treated with efgartigimod reached minimal improvement (TIS ≥20) in a median of 30 days, compared to 72 days for placebo.
- For moderate improvement (TIS ≥40), the median time was 16 weeks for efgartigimod patients. No majority of placebo patients reached this threshold during the study.
Safety Profile:
Efgartigimod was well-tolerated in this patient population, with treatment-emergent adverse events (TEAEs) occurring at similar rates in both treatment and placebo arms. No new safety concerns were identified.
Dr. Hector Chinoy, study investigator and Professor of Rheumatology and Neuromuscular Disease at The University of Manchester, emphasized the significance of the findings: “Myositis is a progressive and debilitating disease with limited treatment options and considerable burden on patients. The ALKIVIA data suggest that FcRn inhibition offers a novel and potentially transformative approach. Efgartigimod not only showed significant clinical improvement but also was well-tolerated — a critical factor for long-term treatment.”
The Phase 3 portion of the ALKIVIA trial is currently ongoing and will provide further validation of these promising interim results.
Sjogren’s Disease: RHO Study Shows Multidimensional Efficacy
In the Phase 2 proof-of-concept RHO study, efgartigimod was evaluated in patients with primary Sjogren’s disease, a complex autoimmune disorder characterized by dryness, fatigue, and systemic organ involvement. The study employed a novel composite endpoint — CRESS — integrating multiple domains of disease activity.
Composite and Symptom-Specific Outcomes:
- CRESS Endpoint Achievement:
- 45.5% of patients on efgartigimod achieved CRESS endpoint success at Week 24, compared to 11.1% in the placebo group.
- Improvements were noted in 4 out of 5 CRESS measures, including systemic disease activity, salivary and tear gland function, and symptom burden.
- ClinESSDAI Scores:
- Patients treated with efgartigimod showed a median reduction of -7.0 in their total clinESSDAI scores (a measure of systemic disease activity), versus -4.0 in the placebo group.
- cSTAR Response:
- Another key composite endpoint, cSTAR, demonstrated a 54.5% response rate in the efgartigimod group, compared to 33.3% in placebo.
Biomarker and Mechanistic Insights:
The RHO study also revealed compelling biomarker shifts supporting efgartigimod’s mode of action:
- Sustained IgG Reduction: Approximately 60% reduction in total IgG levels was observed from Week 4 onward.
- Autoantibody Declines:
- Anti-Ro52 levels decreased by 57% (vs. a 13% increase in placebo).
- Rheumatoid factor dropped by 26.6% (vs. 5.3% in placebo).
- Immune Complex Clearance:
- C1Q immune complexes reduced by 4.5 mc eq/mL in the efgartigimod group, compared to 0.06 mc eq/mL in placebo.
These results suggest that FcRn blockade with efgartigimod may modulate disease biology by lowering pathogenic antibody levels and immune complex formation.
Dr. Isabelle Peene, rheumatologist at Ghent University Hospital and study investigator, highlighted the implications: “Targeting FcRn and reducing IgG autoantibodies appear to have meaningful clinical impact in Sjogren’s disease. The combination of symptom relief, systemic improvement, and favorable biomarker trends signals a promising new avenue for a disease that lacks effective, targeted treatments.”
As with myositis, efgartigimod demonstrated a favorable safety profile in Sjogren’s patients, with no new adverse signals identified. The pivotal Phase 3 UNITY trial is currently underway to further evaluate efficacy and safety in a larger Sjogren’s patient cohort.
Precision Immunology in Rheumatology
The EULAR 2025 presentations reinforce efgartigimod’s potential as a first-in-class FcRn antagonist capable of delivering targeted treatment benefits in complex autoimmune diseases beyond its approved indications. With Phase 3 programs in progress for both myositis and Sjogren’s disease, argenx continues to expand its immunology portfolio into areas of high unmet need.
“These results are not just clinical milestones,” said Dr. Truyen, “they represent progress in redefining how we approach autoimmune diseases — by going deeper into biology and designing smarter, more focused therapies that offer lasting benefit to patients.”
As the field of precision immunology continues to evolve, argenx stands at the forefront, pioneering novel mechanisms that could change the standard of care for patients worldwide.
