After an interim analysis indicated a low probability of efficacy, Sanofi decided to stop early an advanced phase trial on a treatment for a rare autoimmune disease. The decision concerns riliprubart, an antibody developed for chronic inflammatory demyelinating polyneuropathy (CIDP), and reignites attention on the French group’s pipeline, already under scrutiny due to a series of mixed clinical results and the need to strengthen internal development of new therapies.
THE PROGRAM AND THE EARLY STOP
The halted study was part of the phase 3 MOBILIZE program, where riliprubart was evaluated in patients with CIDP refractory to standard treatments. The analysis conducted by an independent data monitoring committee found no safety issues but highlighted that it was “unlikely” the treatment would provide “sufficient efficacy,” leading to the early suspension of the trial.
The drug, reports Fierce Biotech, was compared to placebo over a 24-week period in about 140 patients who had not responded to immunoglobulins or corticosteroids.
SANOFI’S FAILED PLAN
Sanofi had initiated two phase 3 studies in 2024 based on interim data suggesting a potential role for the candidate as a subcutaneous alternative to intravenous immunoglobulins. The trials were designed to include different populations of patients with CIDP, aiming to evaluate clinical responses in contexts of varying sensitivity to available treatments.
ASSESSMENT OF ONGOING STUDIES
After the halt of MOBILIZE, Sanofi stated that the continuation of a second phase 3 study, called VITALIZE, will be evaluated, in which riliprubart is compared to intravenous immunoglobulins in patients already responsive to standard therapy and undergoing stable maintenance treatment. The company also indicated that the study’s cessation will not have significant impacts on costs or financial forecasts for 2026.
WHAT WENT WRONG
According to Fierce Biotech, in the phase 2 program, at the end of week 24, 87% of patients on standard treatment were improved or stable after switching to riliprubart. However, the results obtained in patients unresponsive to standard treatments did not translate into sufficient evidence in the subsequent clinical development phase, with phase 3 failing to confirm initial expectations.
The trials were initially scheduled to provide data during the year, but timelines were revised due to slower than expected enrollment. Subsequently, changes to the screening process improved recruitment speed, with an internal assessment indicating optimism about the drug’s effects on clinical outcomes, according to R&D head Houman Ashrafian during a first-quarter earnings call.
A SERIES OF UNFORTUNATE EVENTS
The halt is part of a series of clinical failures that have affected Sanofi’s pipeline in recent years. Among these, Fierce Biotech recalls amlitelimab, an anti-OX40L antibody that failed to meet endpoints in a phase 2 asthma study; balinatunfib, an oral TNF inhibitor that missed endpoints in a mid-stage psoriasis study; and itepekimab, developed with Regeneron, which failed one of two phase 3 studies in COPD.
The overall picture has been intertwined with tensions in corporate governance, which led to the removal of former CEO Paul Hudson after acknowledging a path described as “bumpy” for 2025, characterized by several unfavorable clinical results.
COMPETITORS’ RESULTS
In the competitive landscape of CIDP, several companies are developing alternative approaches. Argenx has already obtained approval from the Food and Drug Administration (FDA) for Vyvgart Hytrulo and is advancing studies on a C2 inhibitor. Dianthus Therapeutics is developing claseprubart, a C1 inhibitor in phase 3, citing Sanofi’s phase 2 data as support for the target’s relevance, while also claiming that results from their open-label study indicate a potentially superior efficacy profile compared to riliprubart.
WHAT ANALYSTS SAY
Analysts have interpreted the suspension of the riliprubart study as a further sign of development difficulties affecting Sanofi’s pipeline, though with impacts considered more strategic than immediately financial. Graham Parry of Citi called the news “disappointing,” emphasizing how it reinforces the need for a relaunch of R&D under Sanofi’s new management.
From a medium-term perspective, some analyses reported by investment firms like Guggenheim Securities had included riliprubart among assets potentially capable of generating value in the coming years, estimating a potential contribution to sales around 480 million euros by 2033, confirming that the program was considered relevant in building future growth despite the negative phase 3 study outcome.
THE STOCK MARKET REACTION
The market reacted with modest but negative moves in early trading in Paris, where Sanofi shares recorded a drop of up to about 1.5% before recovering part of the losses during the session. The decline was interpreted as consistent with a limited impact on the company’s overall value but signaling pressure on the pipeline at a time when investors are closely monitoring the group’s ability to offset future revenue erosion related to key flagship drugs.
