A Study to Evaluate the Safety and Efficacy of ASP015K in Moderate to Severe Rheumatoid Arthritis

Subjects will take ASP015K or matching placebo orally with food for 12 weeks after randomization. Potential subjects who have previously used disease-modifying antirheumatic drugs (DMARDs) and/or biologic agents may be eligible to participate after completing a washout period. Subjects who complete the 12-week dosing period in this study may be eligible to participate in a long-term, open-label Extension Study.