Approximately 210 subjects will be enrolled in the open label run in phase. Among subjects with polyarticular course JIA, stratification will target at least 50% with a baseline CRP above the upper limit of normal. The first cohort (ie, polyarticular course JIA) will have at least 170 subjects enrolled in the run in phase with the minimum number of JIA categories as follows: 24 with extended oligoarthritis, 20 with polyarthritis RF+, 62 with polyarthritis RF-, 20 with systemic JIA with active arthritis but without active systemic features. Additional cohorts (ie, psoriatic and enthesitis related arthritis) will include a minimum of 20 subjects with psoriatic arthritis, and 20 subjects with enthesitis related arthritis. The overall target minimum number of subjects to be enrolled in the study by age is as follows: 20 subjects 2 to <6 years, 20 subjects 6 to <12 years, and 20 subjects 12 to <18 years. The duration of subject participation among those who complete the study (without discontinuation) is expected to be approximately 44 weeks.