A Study to Determine the Safety and Efficacy of LX3305 in Subjects With Active Rheumatoid Arthritis

Inclusion Criteria: * Adult subjects, aged 18 to 75 years * Active rheumatoid arthritis (RA), class I to III (defined by the American College of Rheumatology), diagnosed at least 3 months prior to Screening * Minimum of 4 swollen joints (at Screening and Day 1), minimum of 4 tender joints (at Screening and Day 1), and serum C-reactive protein (CRP) level \>1.2x the upper limit of normal and/or elevated erythrocyte sedimentation rate (ESR) * If receiving methotrexate (7.5 mg to 25 mg/week), subject must have been treated for at least 6 weeks prior to Screening and currently receiving a stable dose of methotrexate (MTX) with a stable route of administration, and have no plans to change MTX dose during the study * Ability to give written informed consent Exclusion Criteria: * Women who are pregnant or nursing * RA diagnosis prior to 16 years of age (juvenile RA) * Intra-articular and/or parenteral corticosteroids within 4 weeks of study Day 1 * Receipt of live vaccine within 4 weeks prior to Day 1 * Major surgical procedure within 8 weeks prior to Day 1 * Blood donation within 4 weeks prior to Day 1 * Any systemic inflammatory condition * History of bleeding diathesis * History of medically significant opportunistic infection * History of drug or alcohol abuse within 3 years prior to Day 1 * History of cancer within 5 years prior to Day 1 * Presence of hepatic or biliary disease * History of tuberculosis * History of human immunodeficiency virus (HIV) * Any clinically significant laboratory test results, in the opinion of the investigator * Use of any investigational agent or participation in an investigative trial within 30 days of Day 1 * Concurrent use of any biologic agent for the treatment of RA or concomitant disease modifying antirheumatoid drugs (other than MTX, hydroxychloroquine, leflunomide, and sulfasalazine - at stables doses for 8 weeks)