To be sure you are a good fit for the study, there will be 3 visits over the first 8 weeks. The treatment period lasts for another 12 weeks. During this time, every participant will receive the study drug (one of two doses) through an IV in the arm every 2 weeks (total of 6 times). There is no placebo in this study. After each IV dose, we will measure the amount of the drug in your blood over the course of a few hours - this helps us to know how your body is working to process it. There is then a follow-up period which involves 4 visits over 2.5 months. Visits over the course of the study will include blood and urine collection, vital sign measurements, physical exam, electrocardiogram (EKG), questionnaires, demographic questions and review of medications. Some visits will require that you fast (don't eat for an amount of time) beforehand.