Study to assess changes in synovial tissue before and after treatment with Abatacept in subjects with RA who remained on their background disease modifying anti-arthritis medications but who have failed previous therapy with anti-TNF (tumor necrosing factor)blocking agents.

Inclusion Criteria:

• RA for at least 1 year
• Clear clinical signs of active RA in 1 knee joint
• Meet ARA (1987) criteria for diagnosis of RA and ACR (1991) criteria for RA functional classes I, II, or III
• Inadequate clinical response to a minimum of 3 months of therapy with anti-TNF-blocking agents
• Taking background DMARDs for a minimum of 3 months and at stable doses for at least 28 days

Exclusion Criteria:

• Serious bacterial infection in last 3 months
• History of TB
• History of cancer within 5 years
• Evidence of latent or active bacterial or viral infection
• Intra-articular corticosteroids within 3 months
• Exposure to live vaccines
• Exposure to CTLA4Ig or BMS-188667
• Treatment with immunoadsorption column(s), mycophenolate mofetil, leflunomide, anakinra, cyclosporine, etanercept, adalimumab, infliximab, azathioprine, oral or parenteral gold, D-penacillamine, calcineurin inhibitors, cyclophosphamide or other alkylating agents