A Study to Evaluate the Efficacy and Safety of Ocrelizumab in Adults With Primary Progressive Multiple Sclerosis

The screening phase will last up to 24 weeks. In the double-blind treatment phase, participants will undergo at least 120 weeks of study treatment. Study drug (ocrelizumab or placebo) will be administered every 24 weeks. In the FU1 phase, all participants who discontinue prematurely from the double-blind treatment phase will enter the FU1 phase, including participants who receive post-double progression ocrelizumab (PDP OCR) treatment, other immunomodulatory or immunosuppressive treatment(s) for MS, commercial ocrelizumab, or no treatment. The FU1 phase will run in parallel with the double-blind treatment phase until the primary analysis is performed. If the primary analysis is positive, an optional OLE phase is planned for eligible participants who either have remained in the double-blind treatment phase or are on PDP OCR treatment at the time of the primary analysis and, in the opinion of the investigator, could benefit from ocrelizumab treatment. The follow-up 2 (FU2) phase will begin after the primary analysis is performed. The following participants will move into the FU2 phase: participants who are ongoing in the FU1 and not on PDP OCR treatment at the time of primary analysis; participants who are ongoing in the double-blind treatment phase or receiving PDP OCR at the time of the primary analysis and do not enter the OLE phase; participants who complete or withdraw from the OLE phase. At the end of the FU2, all participants will move into B-cell monitoring (BCM) phase until the end of the study. This study will end when all participants who are not being treated with an alternative B-cell depleting therapy have repleted his or her B-cells.