RItuximab Long-Term DOSE Trial in Multiple Sclerosis - RIDOSE-MS

Inclusion criteria: * Diagnosis of Relapsing Remitting MS according to the 2017 revised McDonald criteria OR one demyelinating episode in conjunction with at least one asymptomatic high intensity T2 lesion with size and location compatible with MS * The patient has completed the RIFUND-MS trial and is treated with either of the study medications rituximab or DMF at the last visit of the RIFUND trial OR has been treated with rituximab with a dose regimen of 500 - 1000 mg followed by 500 mg every 6 months for up to two years as part of clinical practice * Age 20 - 52 years (inclusive) * EDSS 0 - 5,5 (inclusive) * The patient is willing and able to give written informed consent, according to the judgement of the investigator. * In fertile females, willing to comply with effective contraceptive methods. These include birth control pills, surgical sterilization of patient or partner or intrauterine device. Non-fertile women is defined as more than 12 months of amenorrhea without an alternative medical cause or, in case of ambiguities, an FSH level in the postmenopausal range. Exclusion criteria: * Diagnosis of Progressive MS * Previous treatment with any "second-line" immunomodulatory drug, eg natalizumab, alemtuzumab, fingolimod, or other long-acting immunosuppressive agents. * Pregnant or lactating women s-HCG will be tested on all women at screening, before each study-related infu-sion and in any situation where there is a reason to suspect pregnancy during the trial, e.g delayed menstrual period more than five days above expected time. * Patients having contraindication for or otherwise not compliant with MRI investigations * Simultaneous treatment with other immunosuppressive drugs * Active, severe infections Signs of infections are assessed before inclusion and each study-related infusion through clinical examination and further evaluated by laboratory and other relevant investigations in case of suspected ongoing infection. Hepatitis serology (HBsAg and anti-HBc) will be evaluated before treatment onset if not tested within the previous three years. * Severe cardiac disorder, e.g signs of congestive heart failure or coronary artery disease. This will be evaluated through clinical assessment before inclusion. * Vaccination within 4 weeks of first dose of study medication. * Documented allergy or intolerance to the IP * Severe psychiatric condition