Vanda's Imsidolimab Receives EU Orphan Designation for Rare Skin Disease GPP

The European Commission (EC) has granted orphan designation to imsidolimab, Vanda Pharmaceuticals' investigational treatment for generalized pustular psoriasis (GPP), based on a positive opinion from the European Medicines Agency's Committee for Orphan Medicinal Products, the company announced August 24, 2026.¹ This marks the first time the EC has granted orphan designation to a drug for GPP in the European Union (EU), according to the company.¹

"The European Commission's Orphan Designation for imsidolimab represents an important milestone for the GPP community and for our efforts to bring this investigational therapy to patients in Europe," said Mihael H. Polymeropoulos, MD, Vanda's president, CEO, and chairman of the board, in a company press release.¹ "With orphan designations now received in Europe, the United States and Japan, we remain focused on advancing imsidolimab for patients in these markets who need new treatment options."

Why is GPP considered a rare, serious disease?

GPP is a severe, chronic, and potentially life-threatening inflammatory skin disease driven by dysregulation in the interleukin-36 (IL-36) signaling pathway and is clinically distinct from plaque psoriasis. It is characterized by widespread pustular eruptions and systemic inflammation. In a nationwide inpatient cohort of 1516 patients in Japan, GPP was associated with serious complications and increased mortality risk.²

Regional variation in GPP prevalence has also been documented within Japan, underscoring how genetic and environmental factors may influence disease frequency across populations.³ To qualify for EU orphan designation, a condition must affect fewer than 5 in 10,000 people; benefits of the designation include protocol assistance, reduced regulatory fees, and market exclusivity provisions following approval.¹

How does imsidolimab work, and what clinical data support it?

Imsidolimab is a fully humanized IgG4 monoclonal antibody that inhibits IL-36 receptor signaling, addressing a deficiency in the endogenous IL-36 receptor antagonist commonly observed in patients with GPP. In the pivotal phase 3 GEMINI-1 trial (NCT05352893), a double-blind, placebo-controlled study of 45 patients ages 18 to 80 experiencing a GPP flare, a single intravenous dose of imsidolimab produced significantly higher rates of disease clearance at 4 weeks compared with placebo, with no serious adverse events leading to treatment discontinuation through 104 weeks of treatment.⁴ Findings from that pivotal study are included in imsidolimab's biologics license application (BLA) for GPP, which is currently under FDA review with a target action date of December 12, 2026.¹

What's next for imsidolimab?

The EU orphan designation follows earlier orphan drug designations for imsidolimab from FDA and Japan's Ministry of Health, Labour and Welfare.¹ Vanda holds an exclusive global license to develop and commercialize imsidolimab, and regulatory and patent exclusivity for the drug is expected to extend into the late 2030s, according to the company.¹

What are the limitations?

Orphan designation facilitates development incentives but does not indicate that imsidolimab will ultimately receive marketing authorization in the EU. The pivotal trial supporting the BLA had a modest sample size and limited long-term placebo comparisons.

References

1. Vanda Pharmaceuticals. Vanda Pharmaceuticals granted orphan designation for imsidolimab for the treatment of generalized pustular psoriasis by the European Commission. Press release. Published August 24, 2026. Accessed August 24, 2026. https://vandapharmaceuticalsinc.gcs-web.com/node/17131/pdf

2. Miyachi H, Konishi T, Kumazawa R, et al. Treatments and outcomes of generalized pustular psoriasis: a cohort of 1516 patients in a nationwide inpatient database in Japan. J Am Acad Dermatol. 2022;86(6):1266-1274. doi:10.1016/j.jaad.2021.06.008

3. Fujita H, Iwasaki R, Tsuboi S, Murashima Y, Akiyama M. Regional differences in the prevalence of generalized pustular psoriasis in Japan. J Dermatol. 2024;51(3):380-390. doi:10.1111/1346-8138.17089

4. Smieszek S, Przychodzen B, Tyner C, et al. Efficacy and safety of imsidolimab for generalized pustular psoriasis. NEJM Evid. 2026;5(5):EVIDoa2500272. doi:10.1056/EVIDoa2500272