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:

1. 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
2. Naïve to any targeted (biologic or nonbiologic) disease-modifying antirheumatic drugs (DMARDs), conventional synthetic DMARDs other than methotrexate (MTX), or investigational therapies for RA
3. 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
4. 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
5. At least a Disease Activity Score 28-joint count calculated using C-reactive protein (DAS28-CRP) ≥ 3.2 at screening
6. At least 3 tender and at least 3 swollen joints at screening and at randomization

Exclusion Criteria:

1. Women who are breastfeeding
2. 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
3. History of or current inflammatory joint disease other than RA (e.g., psoriatic arthritis, gout, reactive arthritis, Lyme disease)
4. At risk for tuberculosis
5. Recent acute infection
6. History of chronic or recurrent bacterial infection (e.g., chronic pyelonephritis, osteomyelitis, bronchiectasis)
7. History of infection of a joint prosthesis or artificial joint
8. History of systemic fungal infections (such as histoplasmosis, blastomycosis, or coccidiomycosis)
9. History of primary immunodeficiency
10. Current clinical findings or a history of a demyelinating disorder
11. 5 or more joints cannot be assessed for tenderness or swelling

Other protocol-defined inclusion/exclusion criteria apply