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

Inclusion Criteria:

• Subject has received a full explanation of the study drug and this study in advance, and written informed consent to participate in the study has been obtained from the subject himself/herself
• Outpatient has RA that was diagnosed according to the 1987 revised criteria of the ACR at least 6 months prior to screening

• At screening subject has active RA as evidenced by all of the following:

  • ≥ 6 tender/painful joints;
  • ≥ 6 swollen joints;
  • CRP of ≥ 0.5 mg/dL or ESR of ≥ 28 mm/h.C-Reactive Protein (CRP) of ≥ 0.8 mg/dL or Erythrocyte Sedimentation Rate (ESR) of ≥ 28 mm/hr
• Subject meets the ACR 1991 Revised Criteria for the Classification of Global Functional Status in RA, Class I, II or, III at screening

Exclusion Criteria:

• Positive tuberculin (TB) test within 90 days of Screening
• Abnormal chest x-ray indicative of an acute or chronic infectious process or malignancy
• Receipt of live or live attenuated virus vaccination within 30 days prior to the first dose of study drug
• Hepatitis B virus or hepatitis C virus carrier or has a history of a positive test for human immunodeficiency virus (HIV) infection
• Any other autoimmune rheumatic disease, other than Sjogren's syndrome
• Previous history of clinically significant infections or illness (requiring hospitalization or requiring parenteral therapy) within 90 days of the Screening visit, or a history of any illness that would preclude participation in the study
• History of any malignancy, except for successfully treated basal or squamous cell carcinoma of the skin or in-situ carcinoma of the cervix
• Does not meet specified washout criteria for the following RA medications: etanercept, certolizumab, adalimumab, golimumab, infliximab and tocilizumab, rituximab, abatacept, anakinra, methotrexate, sulfasalazine, hydroxychloroquine, gold, penicillamine or leflunamide
• Previous intolerance to Janus kinase (JAK) inhibitors
• Receipt of intra-articular or parenteral corticosteroid within 28 days prior to the first dose of study drug
• Receipt of plasma exchange therapy within 60 days prior to the start of study drug
• Receipt of any investigational agent within 30 days or 5 half-lives, whichever is longer, prior to first dose of study drug
• Receipt of medications that are CYP3A substrates with narrow therapeutic range within 14 days prior to first dose of study drug
• History of heart failure, defined as New York Heart Association (NYHA) grade 3 or greater