Abatacept for SLE Arthritis (IM101-330)

This research trial is for patients who have been diagnosed with systemic lupus erythematosus (SLE) with swollen, tender joints (which is called inflammatory polyarthritis) because of the SLE. The purpose of this clinical research study is to evaluate the safety and effectiveness of treatment with abatacept (Abatacept) 125mg injected subcutaneously (under the skin) weekly for 16 weeks versus placebo injections(a substance with no active ingredients and therefore may have no treatment benefit) in subjects with SLE and inflammatory polyarthritis. The effectiveness will be assessed primarily by the number of swollen, tender joints (called a joint count) at each of study visits. Study Medication Abatacept is approved in the U.S. for treating rheumatoid arthritis by prescription and has not been approved by the U.S. Food and Drug Administration for treating SLE yet. In this study, subjects will receive treatment with either abatacept or placebo once a week for 16 weeks (a total of 16 injections).