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
Key facts
- Drug: Imsidolimab (Vanda Pharmaceuticals)
- Class: Fully humanized IgG4 monoclonal antibody; IL-36 receptor inhibitor
- Indication: Generalized pustular psoriasis (GPP)
- Regulatory status: EU orphan designation granted August 24, 2026 (first for GPP in EU)
- Prior designations: FDA and Japan MHLW orphan drug designations
- US status: BLA under FDA review; target action date December 12, 2026
- Key trial: GEMINI-1 (NCT05352893); phase 3, 45 patients
- Key data: Significantly higher disease clearance at 4 weeks vs placebo; no discontinuations for serious AEs through 104 weeks
- Exclusivity: Regulatory/patent exclusivity expected into late 2030s
- Geography: EU, US, and Japan designations
"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
