Non-inferiority Study of Frexalimab Subcutaneous Administration Compared to Intravenous Administration in Adult Participants With Multiple Sclerosis

Inclusion Criteria: The participant must qualify for inclusion per either Group A or B criteria as detailed below, meeting all the inclusion criteria of the applicable group: Group A (RMS) * The participant must be 18 to 55 years of age, inclusive, at the time of signing the informed consent. * The participant must have been diagnosed with RMS in accordance with the 2017 revised McDonald criteria. * The participant must have an Expanded Disability Status Scale (EDSS) score of ≤5.5 at the first visit (Screening Visit). * The participant must have at least 1 of the following prior to screening: * 1 documented relapse within the previous year OR * 2 documented relapses within the previous 2 years, OR * 1 documented Gd enhancing lesion on an MRI scan within the previous year. Group B (nrSPMS) * Participant must have a previous diagnosis of RRMS in accordance with the 2017 revised McDonald criteria * The participant must be 18 to 60 years of age, inclusive, at the time of signing the informed consent. * The participant must have a current diagnosis of SPMS in accordance with the clinical course criteria revised in 2013. * The participant must have documented evidence of disability progression observed during the 12 months before screening. * The participant must have an absence of clinical relapses for at least 24 months. * The participant must have an EDSS score between 3.0 and 6.5 points, inclusive, at the first visit (Screening Visit). Participants from Group A and Group B are eligible to be included in the study only if all of the following criteria also apply: \- Contraceptive use by men and women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies. Exclusion Criteria: * The participant has been diagnosed with primary progressive MS according to the 2017 revision of the McDonald diagnostic criteria. * The participant has a history of infection or may be at risk for infection: * Fever within 28 days of the Screening Visit * Presence of psychiatric disturbance or substance abuse * History, clinical evidence, suspicion or significant risk for thromboembolic events, as well as myocardial infarction, stroke, and/or antiphospholipid syndrome and any participants requiring antithrombotic treatment. * Current hypogammaglobulinemia defined by Ig levels (IgG and/or IgM) below the LLN at screening or a history of primary hypogammaglobulinemia. * A history or presence of disease that can mimic MS symptoms. * The participant has a contraindication for MRI. The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.