Sanofi Halts Phase 3 MOBILIZE Trial of Riliprubart in Refractory CIDP, Dragging Down Complement Class Peer Dianthus
On June 10, 2026, Sanofi announced the early termination of its Phase 3 MOBILIZE clinical trial evaluating riliprubart (an investigational humanized IgG4 monoclonal antibody blocking C1s in the classical complement pathway) in patients with chronic inflammatory demyelinating polyneuropathy (CIDP). The decision followed an interim analysis by an independent data monitoring committee, which concluded that the therapy was "unlikely to provide sufficient efficacy" in this patient cohort.
The setback represents a significant blow to Sanofi's late-stage immunology pipeline and has triggered a major market reaction, dragging down shares of peer biotechnology companies developing classical complement pathway inhibitors.
Clinical Trial Design and the Future of VITALIZE
The MOBILIZE trial was designed to evaluate the efficacy and safety of subcutaneous riliprubart compared to placebo over 24 weeks in approximately 140 patients with CIDP who had failed or were refractory to standard-of-care immunoglobulin (IVIg/SCIg) or corticosteroid therapies.
Crucially, Sanofi's clinical program for riliprubart in CIDP consists of two distinct Phase 3 trials:
- MOBILIZE (Refractory Cohort): Terminated early due to lackluster efficacy in patients who had already failed standard-of-care therapies.
- VITALIZE (Maintenance Cohort): This ongoing study is comparing subcutaneous riliprubart to standard intravenous immunoglobulin (IVIg) in patients who are clinically stable on a maintenance dose of IVIg. Sanofi announced that it is currently assessing whether to continue the VITALIZE trial in light of the MOBILIZE futility readout.
Divergent Outcomes and the "Potency Edge" of Dianthus's Claseprubart
Following Sanofi's announcement, shares of Dianthus Therapeutics (NASDAQ: DNTH) plummeted by over 20%. Investors drew immediate parallels because Dianthus is developing claseprubart (DNTH-103), a subcutaneous monoclonal antibody that also targets C1s in the classical complement pathway, and is currently running the Phase 3 CAPTIVATE trial in CIDP.
However, clinical analysts (including those from Guggenheim, Truist, and Raymond James) quickly defended Dianthus, arguing that the market's sell-off was overdone due to critical pharmacological and trial design differences:
- Target Inhibition and Potency: Analysts highlight that claseprubart possesses a significant "potency edge" over riliprubart. Claseprubart is designed with high binding affinity and half-life extension (YTE technology), which allows it to consistently achieve and maintain IC90 target inhibition of the classical complement pathway, a threshold of suppression that riliprubart reportedly cannot maintain.
- Trial Design Differences: The CAPTIVATE trial in CIDP utilizes a randomized-withdrawal design in IVIg-experienced patients, whereas the terminated MOBILIZE trial was a direct placebo-controlled study in highly refractory patients who had already failed immunoglobulins.
Dianthus remains on track to announce topline results from the Phase 3 CAPTIVATE trial in CIDP by the end of 2026.