This is a study of otelixizumab, a monoclonal antibody (MAb) directed against the human lymphocyte antigen CD3 (a protein found on a certain type of white blood cell). This will be an open-label, comparator-controlled, two part study to evaluate the safety and tolerability of otelixizumab in patients with Graves' ophthalmopathy (GO). It will also look to see if otelixizumab affects GO and how it works compared to methylprednisolone (the standard treatment for active GO).