The purpose of this study is to assess the efficacy and safety of CNTO6785 in participants with active rheumatoid arthritis (RA) despite methotrexate (MTX) therapy.

This is a randomized (participants are assigned to treatment by chance), double-blind (participants and study personnel will not know which treatments are being given), placebo-controlled (a placebo appears identical to a study drug but has no active ingredients), multicenter study. The study will consist of 3 phases: a screening phase, a treatment phase, and a follow-up phase. Approximately 250 participants with active RA despite MTX therapy will be randomly assigned to receive placebo or CNTO 6785 during the double-blind treatment phase. The maximum period of active treatment will be 28 weeks. The maximum duration of study participation will be 44 weeks. Participant safety will be monitored throughout the study.

Inclusion Criteria:

• Have a diagnosis of rheumatoid arthritis (RA) (according to the revised 1987 criteria of the American Rheumatism Association) and have had RA for at least 6 months prior to the date of signing the informed consent at screening
• Have active RA defined study as persistent disease activity with both of the following criteria: at least 6 swollen and 6 tender joints using a 66/68 joint count at the time of screening and at baseline; and serum C-reactive protein (CRP) ≥ 0.8 mg/dL at screening or erythrocyte sedimentation rate (ESR) ≥ 28 mm in the first hour at screening or baseline
• Have been treated with and tolerated methotrexate (MTX) treatment at dosages from 7.5 to 25 mg/week, inclusive, for a minimum of 6 months prior to screening and must have a stable MTX dose for a minimum of 6 weeks prior to the first dosing with study agent

Exclusion Criteria:

• Has inflammatory diseases other than RA, that might confound the evaluation of the benefit of study agent therapy
• Has a diagnosis of fibromyalgia
• Has a recent history (within 12 months prior to screening) of uncontrolled, chronic disease including, but not limited to, pulmonary, psychiatric, and metabolic disturbances, cardiovascular, endocrine, neurological, hepatic, gastrointestinal, renal, hematological, or urological diseases that the investigator believes are clinically significant
• At screening, the results of laboratory tests must meet protocol-specified criteria
• Has ever received any approved or investigational biologic agent for a rheumatic indication