The aim of this study is to compare the efficacy, safety profile, pharmacokinetics, pharmacodynamics, and immunogenicity of BCD-281 and the reference drug in subjects with relapsing multiple sclerosis.

The study includes the following periods:

• Screening (not more than 28 days from the date of signing the ICF).
• Double-blind period - Week 0-72.
• Open-label period - Weeks 72-96.
• Follow-up period - Weeks 96-100. The screening examination is aimed at confirming the eligibility of the subjects for the study. After confirming the eligibility, the subject will be randomized with equal probability into one of two groups (BCD-281 and the reference drug).

Inclusion Criteria:

• Provided written ICF to participate in the study.

• Male and female subjects aged 18 to 55 years inclusive at the time of signing the ICF.

• Diagnosis of multiple sclerosis, established in accordance with the McDonald criteria for the diagnosis of multiple sclerosis (2017 revision).

• Relapsing-remitting multiple sclerosis.

• The total EDSS score 0-5.5 inclusive.

• Documentary evidence of the following at the time of signing the ICF:

  1. at least one relapse within the last12 months, and/or
  2. 2 relapses within the last 24 months, and/or
  3. at least 1 T1 Gd+ lesion detected on brain MRI and 1 relapse within 24 months prior to signing the ICF.

• Presence of IgG antibodies to the Varicella-Zoster virus.

• Neurological stability for 30 days prior to signing the ICF.

• Subject's willingness to discontinue previously prescribed DMTs from the day of the first administration of the IP and throughout the study.

• The ability of the subject to follow the Protocol procedures, according to the Investigator.

• Willingness of subjects of both sexes and their sexual partners of childbearing potential to use reliable methods of contraception from the time of signing ICF, throughout the study and for 5 months after the last dose of the drug in this study.

Exclusion Criteria:

• Primary progressive or secondary progressive MS.
• MS duration of more than 10 years with EDSS score of ≤2.0 at screening.
• Malignant form of MS.
• Other medical conditions that can affect the assessment of clinical picture of the MS.
• Inability to obtain high-quality MRI images and/or the presence of contraindications to MRI and the administration of gadolinium-containing contrast agents.
• Any comorbidities requiring treatment with systemic glucocorticoids and/or immunosuppressive drugs for the duration of the study, with the exception of MS.
• History of progressive multifocal leukoencephalopathy.
• Any acute or exacerbated chronic infections detected during screening that may have a negative impact on subject's safety during the study therapy.
• Concomitant diseases and/or conditions that may affect the assessment of the clinical picture of the underlying disease and/or significantly increase the risk of AEs during the study.
• Known alcohol or drug addiction, or current signs of alcohol/drug addiction.
• History of severe depression and/or a Beck Depression Inventory score of ≥16 at screening examination.
• History of a malignant disease within 5 years prior to screening.
• A diagnosis of HIV infection, hepatitis B or C .
• Inability to provide the subject with venous access.
• Pregnancy or breastfeeding, pregnancy planning and oocyte donation throughout the study and for 5 months after the last dose of ocrelizumab.
• A history of severe allergic or anaphylactic reactions to humanized and/or murine monoclonal antibodies.
• A history of using any prohibited medications or treatments defined in the study protocol.
• Abnormal laboratory blood values, as specified in the study protocol.