Sanofi's Riliprubart CIDP Trial Fails for Futility, Triggering Dianthus's Strong Claseprubart Interim Data Release
The race to develop the first complement inhibitor for chronic inflammatory demyelinating polyneuropathy (CIDP) took a dramatic turn in June 2026. A major Phase 3 failure by Sanofi was quickly followed by a strong clinical update from Dianthus Therapeutics, reshaping competitive dynamics and validating distinct drug-design strategies.
Sanofi's MOBILIZE Setback
On June 10, 2026, Sanofi (NASDAQ: SNY) announced that it is stopping its Phase 3 MOBILIZE trial (NCT06290128) evaluating its investigational C1s inhibitor, riliprubart (SAR445088), in adults with CIDP who are refractory to standard-of-care treatments (such as intravenous immunoglobulin - IVIg).
The decision came after an independent Data Monitoring Committee (DMC) conducted an interim analysis and concluded that the trial was unlikely to demonstrate sufficient efficacy. While no new safety signals were identified, the failure represents a major setback for Sanofi's neurology pipeline. Sanofi stated that the future of its other ongoing Phase 3 trial, VITALIZE (NCT06290141) in IVIg-treated CIDP patients, "will be evaluated accordingly."
Market Contagion and Dianthus's Rebound
The news of Sanofi's failure initially sparked concerns that the classical complement pathway is not a viable therapeutic target in CIDP. Shares of Dianthus Therapeutics (NASDAQ: DNTH), which is developing claseprubart (DNTH-103)—another classical complement C1s inhibitor—plummeted by over 20% on June 10, 2026.
However, on June 11–12, 2026, Dianthus aggressively counter-attacked by disclosing highly positive interim responder analysis data from Part A of its ongoing Phase 3 CAPTIVATE trial (NCT06858579) in CIDP, triggering a massive stock recovery.
- High Efficacy Signal: Among the first 40 participants completing the 13-week open-label Part A, 75% (30 patients) were confirmed responders, achieving a clinical improvement of $\ge$1 point on the adjusted Inflammatory Neuropathy Cause and Treatment (aINCAT) disability score.
- Predefined Target Exceeded: This response rate far exceeded the trial's predefined 50% target (20 patients), confirming an early "GO" decision to proceed with Part B of the study.
- Trial Optimization: Supported by an independent Data Safety Monitoring Board (DSMB), Dianthus streamlined the double-blind, randomized withdrawal Part B of CAPTIVATE. They removed the high-dose (600mg) arm to focus solely on the 300mg Q2W subcutaneous dose, reducing the required sample size from 192 to 128 patients. This modification is expected to accelerate the trial's timeline to top-line results.
- Robust Balance Sheet: Dianthus highlighted a cash position of $1.2 billion as of March 31, 2026, providing a financial runway extending into 2030 to fund its clinical programs.
Why Claseprubart Succeeded Where Riliprubart Failed
Biotech analysts and Dianthus's corporate disclosures highlighted key differences in both drug potency and trial design that explain the divergent clinical outcomes:
- In Vitro Potency Disparity: Head-to-head in vitro experiments revealed that claseprubart has an 8-fold higher binding affinity to active C1s (KinExa $K_D$ of 9 pM vs. 75 pM for riliprubart) and is 3x to 12x more potent at blocking the classical complement cascade in functional assays (such as Wieslab and CH50 hemolysis).
- Patient Cohort Terminology & Design: Sanofi's MOBILIZE trial was restricted entirely to treatment-refractory patients, a highly advanced cohort that is notoriously difficult to treat. In contrast, Dianthus's CAPTIVATE trial enrolls a broader, more representative CIDP population, including patients who are stable on standard therapies (SoC-Treated), treatment-refractory (SoC-Refractory), and treatment-naïve (SoC-Naïve).
- Preservation of Lectin Pathway: While both target C1s, Dianthus's biochemical modeling emphasizes that selective active C1s inhibition preserves the alternative and lectin complement pathways, maintaining critical host defenses against encapsulated bacterial infections and avoiding the need for an FDA Boxed Warning or Risk Evaluation and Mitigation Strategies (REMS) program.
This clinical drama also highlights the entrance of other complement competitors. Argenx recently detailed the design of its Phase 3 EMNERGIZE trial (NCT07091630) evaluating empasiprubart (a complement C2 inhibitor) in CIDP, setting up a highly competitive future landscape alongside approved FcRn blockers like efgartigimod.
Verbatim Quotes
- Sanofi Press Release (June 10, 2026):
"This decision follows an interim analysis by an independent data monitoring committee, which determined that the MOBILIZE study is unlikely to provide sufficient efficacy. No safety signals related to riliprubart were identified as part of this interim analysis. The continuation of other ongoing studies with riliprubart, including the VITALIZE phase 3 study (clinical study identifier: NCT06290141) in IVIg-treated patients with CIDP, will be evaluated accordingly."
- Dianthus Therapeutics Form 8-K (June 12, 2026):
"75% response rate in the first 40 Part A completers (vs. a 50% target) supported an early GO decision for claseprubart at 300mg/2mL Q2W, confirmed by an independent DSMB."