 Although the majority of RA patients achieve an amelioration of their RA with older disease modifying agents such as methotrexate and leflunomide, all of these agents provoke adverse events. The newer more active biological agents have a distinct safety profile that includes an increased risk of serious infections. They have an annual treatment expense in the tens of thousands of dollars a year. PRTX-100 may be able to modify the disease course of rheumatoid arthritis with an improved safety profile compared to available agents and a dosing regimen comparable to the therapies currently available. This study is done to describe the adverse event profile of 6 μgkg of PRTX-100 administered IV for longer periods of treatment that might be required for RA therapy. Secondary objectives include: evaluation of the clinical response of subjects with previous administration of PRTX-100; evaluation of anti-PRTX antibody presence and effect on activity; evaluation of Power Doppler ultrasound in the assessment of joint inflammation; and evaluation of biomarkers. 