Riliprubart Receives Orphan Drug Designation in Japan for Chronic Inflammatory Demyelinating Polyneuropathy
Sanofi announced that Japan’s Ministry of Health, Labour and Welfare (MHLW) has granted orphan drug designation to riliprubart, an investigational monoclonal antibody that targets activated C1s in the classical complement pathway, for the treatment of chronic inflammatory demyelinating polyneuropathy (CIDP). This regulatory milestone marks a significant step forward in the potential expansion of therapeutic options for individuals affected by this rare and debilitating neurological disorder.
CIDP is a rare, chronic autoimmune condition that affects the peripheral nervous system, leading to progressive weakness, numbness, impaired coordination, and fatigue. The disease is caused by immune-mediated damage to the myelin sheath surrounding peripheral nerves, and without adequate treatment, it can result in long-term disability. While therapies such as corticosteroids, intravenous immunoglobulin (IVIg), and plasma exchange are available and effective for many, up to 30% of CIDP patients fail to respond adequately to current standard-of-care treatments. Even among those who benefit, many still experience lingering symptoms that reduce their quality of life.
According to estimates, around 4,000 individuals are currently diagnosed with CIDP in Japan. Given the rarity of the disease and the significant unmet medical need it presents, the MHLW offers orphan drug designation to medicines that address rare conditions affecting fewer than 50,000 patients in Japan and for which there are no satisfactory existing treatments or where the medicine provides a significant improvement over current options.
Riliprubart’s mechanism of action centers on selective inhibition of activated C1s, a component of the classical complement pathway, which plays a key role in autoimmune and inflammatory responses. By interrupting this pathway, riliprubart aims to reduce the immune-mediated damage to peripheral nerves that characterizes CIDP. This approach is part of a broader trend in neurology to explore targeted immunomodulation as a strategy to manage complex autoimmune neurological conditions.
Dr. Erik Wallstroem, MD, PhD, Global Head of Neurology Development at Sanofi, highlighted the significance of the designation, stating:
“The orphan drug designation of riliprubart for people living with CIDP in Japan underscores our commitment to applying our deep understanding of the immune system to address rare neurological disorders with significant unmet medical needs. While CIDP therapies exist, many individuals continue to experience debilitating symptoms, including pain, fatigue and weakness. Our ongoing development of riliprubart reflects our dedication to challenging the status quo in neurology with the goal of improving people’s lives.”
Sanofi has been actively advancing riliprubart through clinical development, and recently shared long-term data from a phase 2 trial at the Peripheral Nerve Society (PNS) meeting held in Edinburgh, UK, from May 17–20, 2025. The 76-week sustained efficacy and safety results demonstrated that riliprubart was associated with durable clinical benefit across a broad spectrum of participants with CIDP. These findings support the potential of riliprubart as a long-term treatment option capable of providing consistent relief from symptoms and potentially altering the disease course.
Currently, riliprubart is being evaluated in two pivotal phase 3 clinical trials aimed at further exploring its efficacy and safety in distinct CIDP patient populations:
- MOBILIZE (NCT06290128): This trial is enrolling patients who are refractory to standard-of-care treatments, including corticosteroids and IVIg. These individuals represent a particularly high-need subgroup with limited options.
- VITALIZE (NCT06290141): This study targets patients currently stabilized on IVIg therapy, assessing riliprubart’s potential to maintain disease control while potentially offering a more convenient or better-tolerated alternative.
Both trials are designed to provide rigorous data on riliprubart’s performance in real-world-relevant patient scenarios. Importantly, these studies will also examine patient-reported outcomes and quality-of-life metrics, which are essential for understanding the full impact of the treatment on daily functioning and well-being.
The orphan drug designation granted by the MHLW offers several potential benefits to accelerate riliprubart’s development in Japan, including priority review status, fee reductions, and market exclusivity for a designated period upon potential approval. These incentives are designed to encourage innovation in areas of unmet need and support the development of new treatments for rare diseases.
Sanofi’s continued investment in riliprubart aligns with its broader strategy to develop next-generation immunotherapies for neurological diseases. The company’s pipeline includes multiple candidates targeting immune-mediated neurology, a field that has garnered increasing interest due to the complex interplay between the immune system and the nervous system in disorders like CIDP, multiple sclerosis, and myasthenia gravis.
As riliprubart progresses through late-stage clinical development, the orphan designation in Japan reinforces confidence in its potential to become a first-in-class therapeutic option for CIDP and provides hope to patients who have long awaited new and effective treatment alternatives.
