Safety Study of PRTX-100 With Methotrexate or Leflunomide to Treat Active Rheumatoid Arthritis

Inclusion Criteria: * Active RA with disease duration of not less than 6 months * Concomitant stable methotrexate or leflunomide therapy Exclusion Criteria: * Diagnosis of any other inflammatory arthritis * ACR Functional Classification of IV * Significant systemic involvement secondary to RA (except for secondary Sjogren's syndrome) * History of clincally significant hypogammaglobulinemia, common variable immunodeficiency, or humeral immunodeficientncy * History of active tuberculosis, pro-thrombotic disorder, venous thrombosis requiring anti-coagulation, substance abuse, or serious psychiatric condition * History of allergy or hypersensitivity to aspirin or non-steroidal cyclooxygenase inhibitors, Staphylococcal protein A * History or presence of malignancy (except for surgically treated basal or squamous cell carcinoma of the skin at least 3 months prior to the start of study medication) * Uncontrolled diabetes or Type 1 diabetes * Unstable ischemic heart disease * Serious active or recurrent infection, hepatic cirrhosis, or other medically unstable condition * Systemic autoimmune diseases other than RA (such as systemic lupus erythematosus, scleroderma, inflammatory bowel disease, inflammatory myopathy) * Positive for HIV, hepatitis B surface antigen, or hepatitis C antibody * Pregnant or nursing females * Inadequate hepatic, renal, or hematologic function * Receipt of live vaccine within 5 weeks of start of study medication * Concomitant administration of other biologic or non-biologic DMARDS, corticosteroids, or anti-CD20 antibodies