A Study to Evaluate the Safety, Pharmacokinetics, Pharmacodynamics, and Efficacy of RO7268489 as Add-on Therapy to Ocrelizumab, in Participants With Progressive Forms of Multiple Sclerosis (MS)

Inclusion Criteria: * PMS, in accordance with the revised 2017 McDonald criteria * Expanded disability status scale (EDSS) at screening between 3.0 and 6.0 inclusive Exclusion Criteria: * MS relapse during the 6 months preceding the randomization date * Lack of peripheral venous access * History of alcohol or other drug abuse, in the opinion of the investigator, within 5 years prior to screening * Inability to complete an magnetic resonance imaging (MRI) * Contraindications to ocrelizumab mandatory pre-medications * Treatment with intravenous immunoglobulin (IV Ig) or plasmapheresis within 12 weeks prior to screening