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Primary Objective:

To determine the efficacy of SAR442168 compared to placebo in delaying disability progression in primary progressive multiple sclerosis (PPMS)

Secondary Objectives:

To evaluate efficacy of SAR442168 compared to placebo on clinical endpoints, magnetic resonance imaging (MRI) lesions, cognitive performance, physical function, and quality of life To evaluate safety and tolerability of SAR442168 To evaluate population pharmacokinetics (PK) of SAR442168 in PPMS and its relationship to efficacy and safety To evaluate pharmacodynamics of SAR442168

Study duration will vary per participant in this event driven trial with a treatment duration of approximately 12 to 60 months.

Inclusion Criteria:

• 18 to 55 years of age inclusive

• Diagnosis of PPMS according to the 2017 McDonald criteria

• Expanded disability status scale (EDSS) score between 2.0 to 6.5 points, at screening inclusive

• Positive cerebrospinal fluid oligoclonal bands and/or elevated Immunoglobulin G (IgG) index either during screening or documented previous history.

• Contraceptive use consistent with local regulations for individuals participating in clinical studies

• Participant is eligible to participate if she is not pregnant or breastfeeding, and

At least one of the following conditions applies:

• Is not a woman of childbearing potential (WOCBP) or is a WOCBP and agrees to use an acceptable contraceptive method

• the participant must not have access to ocrelizumab (eg, ocrelizumab not available on the national market or not reimbursed for the approved indication).

• the participant must have access to and be eligible to be treated with ocrelizumab

But: 1) does not tolerate it due to side effects or safety reasons; and/or 2) has

failed ocrelizumab treatment due to perceived lack of efficacy

Exclusion Criteria:

Participants are excluded from the study if any of the following criteria apply:

• Participant has conditions that would adversely affect study participation such as short life expectancy.

• Evidence of infection with human immunodeficiency virus (HIV), transplantation, progressive multifocal leukoencephalopathy (PML), active hepatitis B or C, active or latent tuberculosis or other active infection that would adversely affect study participation.

• Persistent chronic or active or recurring system infection that may adversely affect participation or IMP administration in this study as judged by the investigator

• History of malignancy within 5 years prior to screening.

• History of alcohol or drug abuse within 1 year prior to Screening.

• Hospitalized for psychiatric disease within 2 years prior to Screening.

• Clinically significant laboratory abnormalities (including evidence of liver injury) or electrocardiogram abnormalities at Screening.

• A bleeding disorder or known platelet dysfunction at any time prior to the screening visit.

• A platelet count