Eligibility Criteria:
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
* 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)
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
* 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
* 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