Disappointing Interim Analysis Forces Sanofi to Discontinue Phase 3 MOBILIZE Trial of Riliprubart

In a new company update, Sanofi announced that it will halt its phase 3 MOBILIZE trial (NCT06290128) of riliprubart in adults with chronic inflammatory demyelinating polyneuropathy (CIDP) refractory to standard-of-care therapy after an independent data monitoring committee (IDMC) determined that the study was unlikely to demonstrate sufficient efficacy. The interim analysis identified no riliprubart-related safety signals.¹

With regard to the discontinuation, the company stated that it is coordinating with investigators and study sites to help facilitate appropriate care transitions for enrolled participants. Sanofi also noted that a comprehensive analysis of the trial data is planned to further assess the findings and inform future research in CIDP. In addition, the company indicated that the status of other ongoing riliprubart studies, including the phase 3 VITALIZE trial (NCT06290141) in patients with CIDP receiving intravenous immunoglobulin therapy, will be reviewed in light of the interim results.

The phase 3 MOBILIZE (NCT06290128) and VITALIZE (NCT06290141) studies were designed to evaluate the efficacy and safety of riliprubart in distinct populations of patients with CIDP. MOBILIZE, a placebo-controlled trial, enrolled and randomized 140 patients whose disease was refractory to standard-of-care treatment. VITALIZE, a double-dummy study, enrolled approximately 160 patients receiving intravenous immunoglobulin (IVIg) who continued to experience residual disability and randomized them to riliprubart plus IVIg placebo or IVIg plus riliprubart placebo.

Both trials include a 24-week double-blind treatment period followed by a 24-week open-label extension. Eligible participants were adults with CIDP diagnosed according to the 2021 European Academy of Neurology/Peripheral Nerve Society criteria,² and an Inflammatory Neuropathy Cause and Treatment (INCAT) score of 2 to 9. The primary end point was the proportion of participants achieving at least a 1-point improvement in adjusted INCAT score at week 24, whereas secondary end points assessed additional disability and impairment measures as well as long-term safety outcomes.³

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Riliprubart is an invesigational humanized IgG4 monoclonal antibody that selectively inhibits activated C1s, a serine protease in the C1 complex of the classical complement pathway. This selectivity leaves the lectin and alternative pathways intact, suppressing complement-driven demyelination and axonal damage without broadly impairing immune surveillance.

Riliprubart's development program included a phase 2, open-label study (NCT04658472) which evaluated the therapy in patients with CIDP who were SOC-treated, SOC-refractory, or SOC-naïve. The trial included a 24-week treatment period (Part A) followed by an optional 52-week extension phase (Part B). For the primary end point, researchers assessed relapse in the SOC-treated cohort and treatment response in the SOC-refractory and SOC-naïve cohorts, defined by a 1-point or greater change in adjusted INCAT disability score.⁴

Results from a prespecified interim analysis of Part A showed that 88% of SOC-treated participants either improved or remained clinically stable after transitioning to riliprubart. Among these patients, 44% (11 of 25) demonstrated improvement, whereas 12% (3 of 25) experienced relapse. In the SOC-refractory cohort, 50% (9 of 18) met the predefined response criteria. Investigators also reported improvements across several measures of disability and impairment.

In addition, plasma neurofilament light chain levels showed a trend toward reduction over time. Treatment-emergent adverse events were reported in 60% (15 of 25) of SOC-treated participants and 72% (13 of 18) of SOC-refractory participants, with headache, fatigue, and nasopharyngitis among the most commonly reported events. Researchers reported that 2 deaths occurred among participants with significant underlying comorbidities.

REFERENCES
1. Press Release: Sanofi provides update on MOBILIZE phase 3 study of riliprubart in chronic inflammatory demyelinating polyneuropathy. News release. Sanofi. June 10, 2026. Accessed June 10, 2026. https://www.sanofi.com/en/media-room/press-releases/2026/2026-06-10-05-00-00-3309444
2. Van den Bergh PYK, van Doorn PA, Hadden RDM, et al. European Academy of Neurology/Peripheral Nerve Society guideline on diagnosis and treatment of chronic inflammatory demyelinating polyradiculoneuropathy: Report of a joint Task Force-Second revision. J Peripher Nerv Syst. 2021;26(3):242-268. doi:10.1111/jns.12455
3. Lewis R, Allen J, Merkies I, et al. Phase 3 Trial Designs Evaluating Riliprubart, a C1s-Complement Inhibitor, in Chronic Inflammatory Demyelinating Polyneuropathy [abstract P10-11.027]. Neurology. 2024. doi:10.1212/WNL.0000000000208529
4. Querol L, Lewis R, Hartung H, et al. Preliminary Efficacy and Safety Data from the Phase 2 Trial of Riliprubart (SAR445088), a Humanized Monoclonal Antibody Targeting Complement C1s, in Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) [abstract S15.008]. Neurology. 2024;102(17 suppl 1). doi:10.1212/WNL.0000000000204596