A Study to Compare the Response to Treatment With Abatacept vs Adalimumab, on Background Methotrexate, in Adults With Early, Seropositive, and Shared Epitope-positive Rheumatoid Arthritis and an Inadequate Response to Methotrexate

Inclusion Criteria: * Early rheumatoid arthritis (RA), defined as symptoms of RA that started ≤ 12 months prior to screening and satisfied the American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) 2010 criteria for the classification of RA at some point during the 12-month period * Naïve to any targeted (biologic or nonbiologic) disease-modifying antirheumatic drugs (DMARDs), conventional synthetic DMARDs other than methotrexate (MTX), or investigational therapies for RA * Treated with MTX for at least 12 weeks, with a stable dose of oral or parenteral MTX for at least 4 weeks prior to randomization * Anti-cyclic citrullinated peptide-2 (Anti-CCP-2) test that is \> 3× the upper limit of normal and are positive for rheumatoid factor (RF) according to central lab testing during screening * At least a Disease Activity Score 28-joint count calculated using C-reactive protein (DAS28-CRP) ≥ 3.2 at screening * At least 3 tender and at least 3 swollen joints at screening and at randomization Exclusion Criteria: * Women who are breastfeeding * Autoimmune disease other than RA (e.g., psoriasis, systemic lupus erythematosus \[SLE\], vasculitis, seronegative spondyloarthritis, inflammatory bowel disease, Sjogren's syndrome) or currently active fibromyalgia * History of or current inflammatory joint disease other than RA (e.g., psoriatic arthritis, gout, reactive arthritis, Lyme disease) * At risk for tuberculosis * Recent acute infection * History of chronic or recurrent bacterial infection (e.g., chronic pyelonephritis, osteomyelitis, bronchiectasis) * History of infection of a joint prosthesis or artificial joint * History of systemic fungal infections (such as histoplasmosis, blastomycosis, or coccidiomycosis) * History of primary immunodeficiency * Current clinical findings or a history of a demyelinating disorder * 5 or more joints cannot be assessed for tenderness or swelling Other protocol-defined inclusion/exclusion criteria apply