Sanofi SA (Sanofi (SNY)) announced Wednesday that it's discontinuing its Phase 3 MOBILIZE study of riliprubart in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) who hadn't responded to standard treatments. The decision came after an independent data monitoring committee concluded the study wasn't likely to hit its efficacy targets. Sanofi was quick to note that the review didn't flag any safety concerns with the drug.

CIDP is a rare autoimmune disorder where the body's immune system attacks the myelin sheaths around nerves in the peripheral nervous system, leading to weakness and numbness. It's a tough disease to study, and that's exactly what the MOBILIZE failure highlights.

Sanofi said it will now review the rest of its riliprubart development program, including the Phase 3 VITALIZE trial in CIDP patients on intravenous immunoglobulin (IVIg) therapy, and conduct a detailed analysis of the MOBILIZE data.

Trial Design Headaches in CIDP

William Blair analyst Myles R. Minter pointed out that the MOBILIZE failure underscores the challenges of running parallel-group controlled studies in CIDP populations. That's precisely why Argenx SE (Argenx (ARGX)) initially evaluated its drug Vyvgart using a randomized-withdrawal design in the ADHERE study, he noted. In a randomized-withdrawal trial, all patients get the drug first, and only those who respond are then randomized to continue the drug or switch to placebo. This design can reduce the noise from patients who never respond and make it easier to detect a treatment effect.

Minter also highlighted Dianthus Therapeutics Inc. (Dianthus Therapeutics (DNTH)), which is testing claseprubart in the randomized-withdrawal CAPTIVATE study. He said this trial design may lower risk by addressing diagnostic and enrollment challenges that have plagued CIDP studies.

For Argenx's other CIDP candidate, empasiprubart, Minter noted that the EMVIGORATE and EMNERGIZE studies — expected to report results in the second half of 2027 — share similarities with the riliprubart program. But he cautioned that Argenx's experience running successful CIDP studies and confirming diagnoses shouldn't be underestimated.

What This Means for Vyvgart

Minter added that setbacks among competing therapies could further strengthen Vyvgart's commercial position in CIDP, which he described as one of biotechnology's strongest product launches. With Sanofi's riliprubart out of the picture for now, Vyvgart's dominance in the CIDP market looks even more secure.

Sanofi shares were up 1.12% at $44.06 in premarket trading Thursday, according to market data.