A Phase II Trial to Evaluate the Clinical Efficacy, Safety and Tolerability of MAS825 in Pediatric and Adult Participants With Still's Disease

Inclusion Criteria:

* Age ≥ 1 with a diagnosis of Still's Disease
* Active diseases defined as:
* CRP or ferritin levels greater than ULN, and any of:

  * Fever ≥ 38°C attributed to Still's Disease activity and documented for a number of days prior to Day 1 or
  * Rash attributed to Still's Disease activity or
  * Musculoskeletal involvement: arthritis in a number of joints per ACP criteria for active joint or
  * Serositis or
  * Macrophage activation syndrome activity as defined by ferritin levels and at least one of: platelet count, a biomarker or fibrinogen levels attributed to Still's Disease activity by the investigator
* Intolerance or inadequate response to available biologic therapy

Exclusion Criteria:

* Patients out of weight range
* Ongoing or previous treatment with immunomodulatory drugs

  * A limited number of Still's Disease patients that have previously received MAS825 through a managed access program are permitted on the study
* Glucocorticoid dose exceeding a set limit
* Any conditions or significant medical problems which places the patient at unacceptable risk for MAS825 therapy

  * Still's disease patients with evidence of macrophage activation syndrome are permitted in the study
  * Still's Disease patients with evidence of interstitial lung disease including those requiring supplemental oxygen therapy are permitted in the study
* History of ongoing, chronic or possibly recurrent infection (e.g. HIV, TB, HCV, HBV) and/or symptoms and signs of clinically significant active bacterial, fungal or viral infections
* Live vaccinations within a set time prior to MAS825 treatment. Live vaccines are prohibited up to several months following the last dose
* History of malignancy of any organ system, including post-transplant lymphoproliferative disorder, treated or untreated, within a number of years, regardless of whether there is evidence of local recurrence and metastases
* History of hypersensitivity to any of the study drugs or to drugs of similar chemical classes or to any of the excipients
* Pregnant or breastfeeding women
* Women of child-bearing potential who do not agree to comply with required contraceptive use

Other protocol-defined inclusion/exclusion criteria may apply.