Inclusion Criteria:

• Males and females ages 18-75 years
• Meet the criteria of the American College of Rheumatology for RA (Arnett FC et al. Arthritis Rheum 1988;31:315-324; refer to Appendix 1. diagnostic criteria for Rheumatoid Arthritis)
• Not bed- or wheelchair-bound
• Active RA, as indicated by the presence of (a) >=6 swollen joints (28 joint count); AND (b) >=6 tender joints (28 joint count); AND either: (c) Westergren ESR of >=28 mm/hour; OR (d) CRP level above the upper limit of normal for the central reference laboratory
• Treatment with weekly oral or parenteral methotrexate for >=6 months prior to baseline
• Methotrexate route of administration has been unchanged for >=2 months prior to baseline
• Dose of methotrexate has been stable at 15-25 mg/week for >=2 months, and is expected to remain stable throughout the study; the stable dose of methotrexate may alternatively be 10-12.5 mg/week if documented toxicity has precluded a higher dose
• If taking hydroxychloroquine or chloroquine, administration duration has been for >=3 months and dose has been stable for >=2 months prior to baseline
• If taking a nonsteroidal anti-inflammatory agent (NSAID), dose has been stable for at least 1 month prior to baseline, and will remain unchanged during protocol participation
• If taking an oral corticosteroid, dose is <10 mg/day prednisone or equivalent, has been stable for at least 1 month prior to the stabilization period, and will remain stable through the stabilization and entire treatment and follow-up period
• Absence of clinically significant findings, such as interstitial pneumonitis or active pulmonary infection, on chest X-ray taken within 6 months prior to screening
• In the Investigator's opinion, the ability to understand the nature of the study and any hazards of participation, and to communicate satisfactorily with the Investigator and to participate in, and to comply with, the requirements of the entire protocol
• Negative screening serum pregnancy test for female patients of childbearing potential
• Females of childbearing potential must utilize, throughout the course of the trial, 2 methods of contraception deemed adequate by the Investigator (for example, oral contraceptive pills plus a barrier method)
• All aspects of the protocol explained and written informed consent obtained

Exclusion Criteria:

• Receipt of any of the following for at least a 1 month stabilization period prior to dosing: sulfasalazine, oral or injectable gold, azathioprine, minocycline, penicillamine, anakinra
• Receipt of etanercept for at least a 6 week period prior to dosing
• Receipt of cyclosporine, infliximab or adalimumab for at least a 2 month period prior to dosing
• Receipt of leflunomide for at least a 2 month period prior to screening, unless patient has undergone cholestyramine washout at least 1 month prior to dosing
• Receipt of cyclophosphamide for at least a 6 month period prior to dosing
• Receipt of rituximab at any previous time
• Participation in a previous trial CF101 trial
• Use of oral corticosteroids >10 mg of prednisone, or equivalent, per day
• Change in NSAID dose level for 1 month prior to dosing
• Change in oral corticosteroid dose level during the 1 month prior to, or during, the stabilization period vChange in hydroxychloroquine or chloroquine dose level during the 2 months prior to, or during, the stabilization period
• Receipt of parenteral or intra-articular corticosteroids during the 1 month prior to, or during, the stabilization period
• Presence or history of uncontrolled asthma
• Presence or history of uncontrolled arterial hypertension or symptomatic hypotension
• Significant cardiac arrhythmia or conduction block, congestive heart failure, or any other evidence of clinically significant heart disease; other clinically significant findings on screening electrocardiogram (ECG)
• Hemoglobin level <9.0 gm/dL at the screening visit
• Platelet count <125,000/mm3 at the screening visit
• White blood cell count <3000/mm3 at the screening visit
• Serum creatinine level outside the central laboratory's normal limits at the screening visit
• Liver aminotransferase (ALT and/or AST) levels greater than 1.25 times the central laboratory's upper limit of normal at the screening visit
• Known or suspected immunodeficiency or human immunodeficiency virus positivity
• Pregnancy, lactation, or inadequate contraception as judged by the Investigator
• Participation in another investigational drug or vaccine trial concurrently or within 30 days prior to screening
• History of drug or alcohol dependence
• History of serious drug or iodine allergy or sensitivity
• History of malignancy within the past 5 years (excluding excised basal or squamous cell carcinoma of the skin)
• Diagnosis of Parkinson's Disease
• Significant acute or chronic medical or psychiatric illness that, in the judgment of the Investigator, could compromise patient safety, limit the patient's ability to complete the study, and/or compromise the objectives of the study