Sanofi’s MOBILIZE phase 3 trial of riliprubart is done. The company ended the study June 10 after an independent data monitoring committee found the C1s-blocking antibody was unlikely to deliver sufficient efficacy in CIDP patients who had already failed immunoglobulin or corticosteroid therapy.
The phase 2 data had looked convincing: 87% of standard-of-care patients improved or stayed stable after switching to riliprubart at week 24. That same population, treatment-resistant patients, looked similar in the midstage study. Phase 3 disagreed. About 140 patients had been enrolled in the 24-week placebo-controlled trial when the DMC called it.
A second phase 3, comparing riliprubart to IVIg in patients responding to standard of care, is still running. Sanofi is assessing whether to continue. That decision now carries the whole commercial ceiling: 2033 riliprubart sales were estimated at 480 million euros ($555M).
This is the latest setback in a run that cost CEO Paul Hudson his job in February 2026. He’d described 2025 as a “bumpy ride” before leaving: amlitelimab flunked a phase 2 asthma trial, balinatunfib missed the goal in midstage psoriasis, itepekimab failed one of two phase 3 COPD studies.
The read-across cuts two ways. Argenx’s Vyvgart Hytrulo already holds FDA approval in CIDP, and it’s running phase 3 with a C2 inhibitor in the same indication. Dianthus Therapeutics has cited Sanofi’s phase 2 as proof of concept for claseprubart, its C1 inhibitor in phase 3, and has argued better response rates — but MOBILIZE raises the mechanism question for that validation. IVIg makers CSL Behring, Grifols, and Pfizer can breathe easier.
Worth tracking Sanofi’s call on the IVIg-comparison trial before year-end.
— Rebecca Lauren