All safety data will be descriptively summarized using corresponding populations. will be provided in a secure data sharing environment. For details on submitting a request, ITGB2 see the instructions provided at www.vivli.org. Abstract Background Juvenile idiopathic arthritis (JIA) is the most common pediatric rheumatic disease and the most common systemic disorder associated with uveitis in childhood. Uveitis is more common in JIA patients who are antinuclear antibody (ANA)-positive, have an early-onset disease, and have oligoarticular arthritis. JIA-associated uveitis (JIA-uveitis) is typically anterior, chronic, bilateral, nongranulomatous, and asymptomatic. Visual outcomes in JIA-uveitis have improved with current screening and treatment options; however, many patients fail to respond or do not achieve long-lasting remission. Baricitinib, an oral selective Janus kinase (JAK)1 and 2 inhibitor, may impact key cytokines implicated in the pathogenesis of JIA-uveitis or ANA-positive uveitis, representing a potential novel treatment option for disease management. Methods The multicenter, phase 3 trial will be conducted using an open-label Bayesian design. The study will enroll at least 20 and up to 40 patients aged 2 to 18 years with active JIA-uveitis or chronic ANA-positive uveitis without systemic features. At least 20 patients who have had an inadequate response or intolerance to methotrexate (MTX-IR), but not biologic disease-modifying antirheumatic drugs (bDMARDs), will be randomized (1:1) to open-label baricitinib or adalimumab. Approximately 20 additional patients who are MTX-IR or bDMARD inadequate responders will receive baricitinib treatment. Patients will be treated with once daily oral baricitinib at a fixed dose by age group (4 mg for patients aged 6 to 18 years and 2 mg for patients 6 years) or adalimumab (20 mg for patients weighing 30 kg and 40 mg for patients 30 kg) as a subcutaneous injection every 2 weeks. Treatment with stable background conventional synthetic DMARDs, low-dose corticosteroids, and/or nonsteroidal anti-inflammatory drugs is allowed. The primary endpoint is the proportion of patients with response at week 24. Patients may continue treatment for up to 5 years. Discussion This is the first pediatric clinical trial to assess the clinical effectiveness and safety of a JAK inhibitor in JIA-uveitis or chronic ANA-positive uveitis. A novel Bayesian design is used to assess the efficacy of baricitinib, including an adalimumab reference arm, in this small patient population with unmet medical need. Trial registration EudraCT 2019-000119-10. Registered on January 4, 2019; “type”:”clinical-trial”,”attrs”:”text”:”NCT04088409″,”term_id”:”NCT04088409″NCT04088409. Registered on September 12, 2019 0.0001) [6]. The ADJUVITE study, a double-blind, randomized, placebo-controlled study, also supports the efficacy of adalimumab in patients with early-onset, chronic, JIA-associated or idiopathic anterior uveitis and an inadequate response to topical steroids and MTX, although the study was small [11]. The phase 2, single-arm (adaptive-trial), open-label APTITUDE trial evaluated the efficacy and safety of the fully humanized anti-interleukin (IL)-6R antibody, tocilizumab, with MTX in anti-TNF refractory JIA-uveitis. While the trial did not pass the prespecified criterion based on the adaptive design, 3-Methyl-2-oxovaleric acid data showed that of 21 patients, 33% had a 2-step improvement in the level of inflammation (anterior chamber cells) at week 12 and a further 14% had a 1-step improvement at week 24 [12]. Despite the increasing usage of biologics in JIA-uveitis, many patients fail to 3-Methyl-2-oxovaleric acid respond to or do not achieve long-lasting remission with these medications. For example, treatment failure occurred in 27% of patients on adalimumab and MTX in the SYCAMORE trial [6]. Furthermore, during a 2-year treatment period, 40% of JIA-uveitis patients receiving adalimumab and 80% receiving the anti-TNF monoclonal antibody, infliximab, did not achieve clinical remission [7]. Baricitinib is an oral selective Janus kinase (JAK) 1 and JAK2 inhibitor with less 3-Methyl-2-oxovaleric acid activity against the JAK family members, tyrosine kinase 2 and JAK3 [13]. Baricitinib modulates cytokine signaling pathways implicated in disease pathogenesis by partially inhibiting JAK1 and JAK2 enzymatic activity, resulting in reduced phosphorylation and activation of signal transducers and activators of transcription (STATs) and reduced inflammation, cellular activation, and proliferation of key immune cells.