This study is evaluating the safety, pharmacokinetics (PK), pharmacodynamics (PD) and efficacy of ACP-196 in subjects with Rheumatoid Arthritis on background Methotrexate.

A multicenter, randomized, double-blind, placebo-controlled, parallel-group clinical trial. The on-treatment period is 4 weeks with weekly visits to the clinic, followed by a 4-week safety follow-up period after the last dose of ACP-196/placebo. The study was to evaluate the safety, PK, PD, and efficacy of ACP-196 in subjects with Rheumatoid Arthritis on background Methotrexate

Main Inclusion Criteria:

• Diagnosis of RA according to the 2010 ACR/EULAR Classification Criteria .
• Must be on a stable MTX dose (7.5 to 25 mg/week)
• Subjects must be able to read and understand the consent form, complete the study-related procedures, and communicate with the study staff.
• Are willing and able to adhere to the study visit schedule, and understand and comply with other protocol requirements.

Main Exclusion Criteria:

• Prior malignancy, except for adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, or other cancer from which the subject has been disease free for ≥ 5 years.
• A life-threatening illness, medical condition or organ system dysfunction which, in the investigator's opinion, could compromise the subject's safety, interfere with the absorption or metabolism of ACP-196, or put the study outcomes at undue risk.
• Subjects who have taken any investigational drug within the previous 30 days before randomization.
• Use of all other synthetic disease-modifying antirheumatic drugs (DMARDS) such as but not limited to leflunomide, azathioprine, cyclosporine, penicillamine or gold salts within 8 weeks of randomization.
• Use of etanercept, anakinra, tofacitinib within 4 weeks of randomization.
• Use of abatacept, humira, infliximab, or tocilizumab within 8 weeks of randomization.