A Study Comparing SB5 to Humira® in Subjects With Moderate to Severe Rheumatoid Arthritis Despite Methotrexate Therapy

Inclusion Criteria: * Are male or female aged 18-75 years at the time of signing the informed consent form. * Have been diagnosed as having RA according to the revised 1987 American College of Rheumatology (ACR) criteria for at least 6 months but not exceeding 15 years prior to Screening. * Have moderate to severe active disease despite MTX therapy defined as: 1. More than or equal to six swollen joints and more than or equal to six tender joints (from the 66/68 joint count system) at Screening and Randomisation. 2. Either erythrocyte sedimentation rate (Westergren) ≥ 28 mm/h or serum C-reactive protein ≥ 10 mg/dL at Screening. * Must have been treated with MTX for a total of at least 6 months prior to Randomisation and must have been on both: a stable route of administration (oral or parenteral) and stable dose of MTX (10-25 mg/week) for at least 4 weeks prior to Screening. * Female subjects who are not pregnant or nursing at Screening and Randomisation and who are not planning to become pregnant from Screening until 5 months after the last dose of IP. Exclusion Criteria: * Have been treated previously with any biological agents including any tumour necrosis factor inhibitor. * Have a known hypersensitivity to human immunoglobulin proteins or other components of Humira or SB5. * Have a positive serological test for hepatitis B or hepatitis C or have a known history of infection with human immunodeficiency virus. * Have a current diagnosis of active tuberculosis (TB), have been recently exposed to a person with active TB, or are considered to have latent TB. * Have had a serious infection or have been treated with intravenous antibiotics for an infection within 8 weeks or oral antibiotics within 2 weeks prior to Randomisation. * Have a history of chronic or recurrent infection. * Have any of the following conditions: 1. History of congestive heart failure (New York Heart Association Class III/IV). 2. History of acute myocardial infarction or unstable angina within the previous 12 months prior to Screening. 3. History of demyelinating disorders. 4. History of any malignancy within the previous 5 years prior to Screening. 5. History of lymphoproliferative disease including lymphoma. 6. Any other disease or disorder which, in the opinion of the Investigator, will put the subject at risk if they are enrolled. * Have physical incapacitation (ACR functional Class IV or wheelchair-/bed-bound).