A Study to Evaluate the Pharmacokinetics, Efficacy and Safety of Intravenous Golimumab in Pediatric Participants With Active Polyarticular Course Juvenile Idiopathic Arthritis Despite Methotrexate Therapy

This is a single arm, Open-label (all people know the identity of the intervention), multi-center (when more than one hospital or medical school team work on a medical research study) study to determine the pharmacokinetics (the study of the way a drug enters and leaves the blood and tissues over time), efficacy (effectiveness) and safety of intravenous golimumab in participants with pJIA despite current treatment with methotrexate (MTX). The study will consist of 3 parts: Screening Phase (6 weeks); an Open-label Treatment Phase (consists of golimumab and MTX treatment for 52 weeks, wherein after Week 28, MTX dose change is allowed); Long-term Extension Phase (after Week 52 through Week 252) and Extended Treatment Period (after week 252). The maximal study duration for a participant will not exceed 832 weeks. All the eligible participants will be administered golimumab IV infusion and commercial MTX. Blood samples will be collected for evaluation of pharmacokinetics of study treatment. Participants' safety will be monitored throughout the study.