Despite the therapeutic improvements with recent biologic agents approved for rheumatoid arthritis, there is still significant unmet medical need for the treatment of subjects with this chronic disease to achieve a faster, more complete response, and higher rates of remission. The aim of the study is to explore the optimum dose of mavrilimumab for further clinical development and more fully investigate the efficacy and safety profile of mavrilimumab after longer drug exposure (that is, 24 weeks). The results of this study will form the basis for future clinical studies with mavrilimumab.