Abatacept vs Placebo in RA Patients With Hepatitis B on Entecavir Background

The purpose of this study is to investigate whether the combination of abatacept along with entecavir (the study drugs) is safe and effective in treating symptoms related to rheumatoid arthritis (RA). Abatacept, given in an intravenous (IV - injected into a vein) as well as subcutaneous form, is approved by the FDA for the treatment of RA. In this research, abatacept will be given by injection. A subcutaneous injection is an injection given under the skin. Entecavir, to be taken by mouth, is approved by the FDA for the treatment of hepatitis B. The study is divided into the following time periods: Screening Phase: Up to 4 weeks Randomized Double-blind Phase: 24 weeks Open-label Extension Phase: 24 weeksFollow-up Phase: a phone call after Week 48 Each phase contains one or more study visits.