A Long-term Extension of Study GNC-401

Main Inclusion Criteria:

1. The patient has given written informed consent to participate in the study;
2. Current diagnosis of RMS, based on the McDonald 2017 criteria ;
3. Patients must have completed study GNC-401. Completion is defined as having performed the Week 48 assessments of study GNC 401;
4. Have no clinical (relapses) or MRI signs (≥2 new T2 lesions of >10 mm diameter) of acute MS disease activity, based on the Week 48 MRI of study GNC 401, or, if yes, been retreated prior to study entry with rituximab;
5. Have a B cell count ≤0.05 x 109 CD19 cells/L (assessed at the end of study GNC 401, or before inclusion in this study GNC 402 (available result from routine clinical practice); if not retreated with rituximab before entering study GNC-402, monthly B-cell count will be executed and retreatment will be considered by the treating physician when B-cells are >0.05 x 109 CD19 cells/L);

Main exclusion criteria

1. The emergence of any disease diagnosis during the course of study GNC-401 that is not due to MS and could better explain the patient's neurological signs and symptoms;
2. Body weight ≤40 kg;
3. Contraindication to continue rituximab therapy;
4. Has received rituximab less than 12 days prior to study entry;
5. Use of any of the following medications since Week 48 of the GNC 401 study:
6. Interferon (IFN) β, glatiramer acetate, IV immunoglobulin (IVIG), dimethyl fumarate or teriflunomide;
7. Natalizumab, mitoxantrone, cladribine, alemtuzumab, cyclophosphamide, systemic cytotoxic therapy, total lymphoid irradiation, and/or bone marrow transplantation;
8. Highly potent immune modulating therapy, such as: ocrelizumab, ofatumumab, fingolimod, siponimod, ozanimod or anti-cytokine therapy, plasmapheresis or azathioprine;
9. Any experimental drugs for the treatment of MS;
10. Common Terminology Criteria for Adverse Events (CTCAE) Grade 2 or greater lymphopenia (based on Week 48 of study GNC 401);
11. Any major medical or psychiatric disorder that would affect the capacity of the patient to fulfill the requirements of the study, including:
12. Diagnosis or history of schizophrenia;
13. Current diagnosis of moderate to severe bipolar disorder, major depressive disorder, major depressive episode, history of suicide attempt, or current suicidal ideation;
14. Current or past (within the last 2 years) alcohol or drug abuse;
15. History or presence of serious or acute heart disease such as uncontrolled cardiac dysrhythmia or arrhythmia, uncontrolled angina pectoris, cardiomyopathy, or uncontrolled congestive heart failure (New York Heart Association [NYHA] class 3 or 4);
16. Known inability to undergo an MRI scan;
17. Contraindications to the use of 5% glucose solution for infusion;
18. Inability to follow study instructions, or complete study assessments, as defined by the protocol;
19. Any history of cancer with the exceptions of basal cell carcinoma and/or carcinoma in situ of the cervix, and only if successfully treated by complete surgical resection, with documented clean margins and any medically unstable condition as determined by the Investigator;
20. Pregnant or breastfeeding women;
21. Abnormal liver function tests: aspartate aminotransferase (AST) or alanine aminotransferase (ALT) >2 times upper limit of normal range (ULN), or conjugated bilirubin >2 times ULN, or alkaline phosphatase (AP) or gamma-glutamyl transferase (GGT) >3 times ULN;