WA16291 is a Phase IIa "proof-of-concept" study. The primary objective of this study is to determine the safety and efficacy of rituximab (a B cell depleting chimeric monoclonal antibody) used either as monotherapy or in combination with methotrexate or cyclophosphamide in participants with rheumatoid arthritis who have failed prior Disease Modifying Anti-Rheumatic Drug (DMARD) therapy and currently have an inadequate clinical response to methotrexate.