Inclusion Criteria:

• Signed informed consent must be obtained prior to any assessment performed.
• Male or female participants aged 18-65 (inclusive) at Screening.
• Diagnosis of SPMS according to the 2017 revised McDonald criteria (Thompson et al 2018) at Screening.
• Absence of documented clinical relapses in the 24 months before Screening and randomization.
• EDSS score of 3.0 to 6.0 (inclusive) at Screening.
• Documented evidence of disability progression in the 12 months before Screening.

Exclusion Criteria:

• Unwilling or unable to undergo MRI scans as per protocol (for example, claustrophobia, or presents absolute contraindications to MRI (e.g., metallic implants, metallic foreign bodies, pacemaker, defibrillator)).
• History of clinically significant central nervous system (CNS) disease (e.g. stroke, traumatic brain or spinal injury, history or presence of myelopathy) or neurological disorders which may mimic multiple sclerosis (MS).
• Ongoing substance abuse (drug or alcohol) or any other factor (e.g. serious psychiatric condition) that may interfere with the participant's ability to cooperate and comply with the study procedures.
• Participants with history of confirmed Progressive Multifocal Leukoencephalopathy (PML) or neurological symptoms consistent with PML.
• Women of childbearing potential (WOCBP), defined as all women physiologically capable of becoming pregnant from menarche until becoming post-menopausal, unless they are using highly effective methods of contraception (failure rate < 1% per year) while taking study treatment and for at least 1 week after stopping study treatment.
• Significant bleeding risk or coagulation disorders, at Screening.
• Use of exclusionary medication prior to Screening/randomization as listed in the protocol.

Other protocol-defined inclusion/exclusion critria may apply