Juvenile Idiopathic Arthritis (JIA) Clinical Trials

• Study informed consent form voluntarily and independently signed by patient legal representative

• Study assent form voluntarily and independently signed by minor study subject (patient)

• Male or female patients aged ≥12 and \<18 years (cohort 1 - subgroup A) or \>2 and \<12 years (cohort 1 - subgroup B) or \>2 and \<18 years (cohort 2) at the time of screening initiation and on Day 0

• Body weight at the start of screening and on Day 0 ≥45 kg (cohort 1 - subgroup A) or ≥30 and \<45 kg (cohort 1 - subgroup B) or ≥18 and \<30 kg (cohort 2)

• A reliable diagnosis of juvenile idiopathic arthritis (JIA) according to the JIA International League of Associations for Rheumatology (ILAR) 1 criteria with onset before the age of 16 years:

‣ Seropositive or seronegative polyarthritis (pJIA) ≥3 months before screening, or

⁃ Systemic JIA (sJIA) for ≥3 months before screening, provided that joint symptoms persist without active systemic manifestations for ≥3 months before screening, or

⁃ Extended oligoarticular JIA (оJIA) ≥3 months before screening

• American College of Radiology (ACR) criteria of active polyarthritis are met: 5 or more active joints at screening and on Day 0

• C-reactive protein (CRP) level on screening or in anamnesis, not associated with alternative causes of increase other than the activity of the underlying disease, ≥6 mg/l

• Intolerance or failure of methotrexate in the dose of ≥15 mg/m\^2/week (or less, in a case of documented intolerance of higher doses) for ≥3 months in medical history