Inclusion Criteria:

• - Age between 18 and 65 years.

• - A diagnosis of relapsing MS according to the 2017 McDonald criteria.

• - Disease activity seen as either a clinical relapse or MRI activity during the last 12 months.

• - EDSS between 0 and 5.5.

• - Thrombocytes and leukocytes within normal range, and lymphocytes above 0.8 x10 9/L before first dose of study medication.

• - A) For women of childbearing potential: accepting to use adequate contraception in the trial period.

If randomized to cladribine, women who use systemic hormonal contraception must accept to use additional barrier contraception during each treatment cycle and for four weeks after each treatment cycle.

• - B) For men: If randomized to cladribine, accepting to use adequate contraception in the safety period of 6 months after each treatment cycle.

• - Able to understand written and spoken Norwegian or English.

• - Able to complete treatment or follow-ups in the study (e.g. no contraindications for MRI, severe psychiatric disease, drug abuse or plans of moving) - Signed informed consent.

Exclusion Criteria:

• - Any contraindication or increased risk of side-effects from rituximab or cladribine (such as ongoing acute or chronic infection, live vaccination less than 4 weeks before start of treatment or planned live vaccination, immunocompromised, previous or active malignant disease, ongoing glucocorticoid treatment or allergy against any products of the medication) - Previous use of any of cladribine, rituximab, alemtuzumab, ocrelizumab, hematopoietic stem cell therapy (HSCT) or other immunosuppression with long lasting effects.

• - Fingolimod or natalizumab treatment within the last six months before inclusion.

- Current pregnancy or lactation

Multiple sclerosis (MS) is a demyelinating and neurodegenerative inflammatory disease of the central nervous system, affecting more than 12 000 patients in Norway and more than 2.2 mill patients worldwide. Oral cladribine is one of the first choices for highly efficient disease modulatory treatment (DMT), while Rituximab is used off-label as DMT in relapsing MS. Large observational studies indicate good tolerance and treatment effect of rituximab in MS and studies from other diseases indicate a good safety profile. However, no phase 3 studies have been performed to test whether rituximab is as efficient as established MS treatments. Formal safety data is also lacking for the treatment with rituximab in MS. The investigators will perform a prospective randomized open-label blinded endpoint multicenter non-inferiority study. The primary objective is to test whether rituximab is non-inferior to oral cladribine in the treatment of relapsing MS. 264 MS patients aged 18-65 years with relapsing MS will be recruited from 10 centers and followed for 96 weeks. The primary endpoint is difference in new T2 lesions between the groups. Furthermore, the investigators will test novel blood sample and MRI biomarkers to provide tools for personalized MS treatments. Finally, the health economic consequences of these treatment options will be evaluated. This study will guide clinicians and patients in the future treatment choice for MS and can potentially make a huge impact on the costs of future MS treatment.

Arms

Active Comparator: Rituximab

Biosimilar rituximab concentrate for solution for infusion

Active Comparator: Cladribine

Mavenclad oral cladribine tablets

Interventions

Biological: - Rituximab

Biosimilar rituximab concentrate for solution for infusion

Drug: - Cladribine

Mavenclad oral cladribine tablets