MabionCD20® Compared to MabThera® and Rituxan® in Patients With Rheumatoid Arthritis

INCLUSION CRITERIA: 1. Male or female, age 18 - 80 years 2. Body Surface Area (BSA) between 1.5 and 2.2 m2 3. Confirmed diagnosis of RA diagnosed according to the revised (2010) ACR/EULAR classification criteria, with a disease duration minimum of 6 months prior to the Screening Visit 4. Currently moderate to severe RA despite ongoing administration of an adequate MTX regimen. Moderate to severe disease is defined here as the presence of the following two criteria: 1. Six or more swollen joints and ≥6 tender/painful joints, verified by a physician during the screening and re-confirmed at baseline visit (Day 1) 2. DAS28 score ≥3.2 at screening 5. No history of treatment with TNF-α inhibitor (innovative or biosimilar, authorized or investigational) at any time before the screening i.e. TNF-α inhibitor naive population. 6. Receiving MTX treatment at a dosage of 7.5-25 mg/week for at least 12 weeks prior to screening, with the last 4 weeks at a stable dose, and willing to remain at this dose for the entire study duration 7. Male or WOCBP must consent to use highly effective contraception, from the Screening Visit, during the intervention period, and for at least 12 months after the last dose of study intervention 8. Female participants must not be pregnant or lactating (negative baseline serum test) EXCLUSION CRITERIA: 1. History of or current inflammatory joint disease other than RA 2. History of or current systemic autoimmune disorder 3. ACR functional class IV disease 4. History of psychiatric disorder that would interfere with normal participation in the study 5. Evidence of HBV, HCV, HIV infection 6. Evidence of laboratory-confirmed or clinically suspected SARS-CoV-2 infection within 14 days before the study drug administration and a documented positive RT-PCR test within 72 hours before the first infusion or positive antigen test within 24 hours before the first infusion. 7. Serious and/or uncontrolled coexisting diseases which are recognized as major contraindications to the administration of rituximab, methotrexate or any of the pre-medication components or as important risk factors for the development of severe or life-threatening SARS-CoV-2 infection or other factors, which in the Investigator's opinion, would preclude patients participation. This category includes severe pulmonary, cardiovascular, neurologic, renal and hepatic diseases, severe and inadequately controlled type 1 or 2 diabetes. 8. Recent history or current evidence of bacterial, viral or fungal infection (excluding infections of nailbeds) 9. History of or current active tuberculosis, with typical symptoms of M. tuberculosis infection confirmed by positive results of TB screening test or documented diagnosis prior to screening 10. Latent tuberculosis, as documented in subject's medical records or shown by a positive or indeterminate QuantiFERON test performed at screening, in absence of typical symptoms of tuberculosis. However, a patient with latent tuberculosis may become eligible for the study if he/she meets the following criteria: 1. Patient completed a standard TB prophylaxis prior to the screening and had no active TB or contact with active TB case after completion of the most recent prophylactic regimen OR received at least four weeks of standard TB prophylactic regimen prior to the screening visit and is capable and willing to continue on this regimen while participating in the study. 2. Patient has no active TB at the time of screening, which must be confirmed through referral to a TB specialist if \> 1 year has passed since the completion of the last prophylaxis or if the prophylaxis is still being received by the time of screening 3. Patient had no positive findings on chest X-ray examination at screening and within three months prior to screening 11. History of cancer (solid tumors, hematologic malignancies and other) within 5 years of the screening 12. History of significant cytopenia or other disorder of the hematopoietic system 13. Primary or secondary immunodeficiency 14. Any other condition that is listed as a contraindication to receive rituximab or methotrexate therapy 15. Recent use of biologic DMARDs or non-biologic DMARDs other than MTX within the washout periods specified in the study protocol 16. Treatment with any of the authorized or investigational TNF-α inhibitors at any time before the screening (regardless if innovative or biosimilar). 17. History of prior treatment with a B cell modulating or B cell depleting therapy such as, but not limited to, rituximab or other anti CD20 mAb (ocrelizumab, ofatumumab, obinutuzumab), belimumab, atacicept, tabalumab, epratuzumab and other experimental treatments 18. Use of systemic glucocorticoids at a dose higher than 10 mg prednisolone daily or equivalent, within 2 weeks prior to Screening or between screening and Day 1 19. Use of intraarticular hyaluronic acid injection within 28 days before the screening or between screening and Day 1. 20. Use of any drug that has not received regulatory approval for any indication within 4 weeks or a minimum of 5 half-lives, whichever is longer, prior to the Screening Visit or planned receipt of unauthorized drug or vaccine during the study. 21. History of prior allergic or anaphylactic reaction to rituximab therapy (or to any excipient contained in the study IMP) 22. Serious abnormal laboratory findings, specifically: 1. White blood cell count \<3,000/μL OR neutrophil count \<1,500/μL. 2. Platelet count \<75,000/μL. 3. Aspartate aminotransferase or alanine aminotransferase \>2.5 times ULN. 4. Hemoglobin \<8.0 g/dL. 5. IgG below 5.0 mg/mL or IgM below 0.4 mg/mL. 6. Any other clinically significant laboratory abnormality. 23. Intolerance or contraindications to administration of MTX therapy, i.v. glucocorticoids, or to any other component of the premedication 24. Major surgery (including joint surgery) within 8 weeks prior to Screening or planned surgery within 12 months after baseline 25. Recent vaccination with inactivated/non-live vaccine (\<4 weeks prior to study intervention infusion on Day 1) or live vaccine (\<6 weeks prior to study intervention infusion on Day 1) vaccine 26. Planned vaccination with live vaccine during the follow-up. 27. Chronic intake of narcotic analgesics (e.g. morphine, fentanyl, hydrocodone, oxycodone, codeine). 28. Participation in a clinical study during the 2 months prior to enrolment in the study (exemption - previously failed screening procedures in MabionCD20-003RA study). 29. Female patients breastfeeding, pregnant or planning of pregnancy within 12 months after the last infusion of the study intervention. 30. Blood donation or other blook loss of more than 500 ml within the last two months prior to Screening Visit. 31. Lack of peripheral venous access. 32. History of drug, alcohol or chemical abuse within 2 years prior to screening.