The purpose of this study is to determine if investigational (not FDA approved) drug AMG570 can be an effective treatment for patients with Systemic lupus erythematosus (SLE) that are not responding well to their current standard of care therapy. This study will compare 3 dose levels with placebo (A placebo looks like the study drug, but the injection does not contain the active ingredient) to determine the ideal therapeutic dose. You will have 32 scheduled visits. Your participation in this study will last approximately 1 year and 5 months consisting of the following: Screening (2 visits); Treatment will be administered (by injection) every 2 weeks for 52 weeks; and safety follow-up (16 weeks).