A Study of Ocrelizumab in Participants With Primary Progressive Multiple Sclerosis

Inclusion Criteria: * Diagnosis of primary progressive multiple sclerosis (according to revised McDonald criteria) * EDSS at screening from 3 to 6.5 points * Disease duration from onset of MS symptoms less than (\<) 15 years if EDSS greater than (\>) 5.0; \<10 years if EDSS greater than or equal to (\>/=) 5.0 * Sexually active male and female participants of reproductive potential must use two methods of contraception throughout the study treatment phase and for 48 weeks after the last dose Exclusion Criteria: * History of relapsing remitting MS, secondary progressive, or progressive relapsing MS at screening * Inability to complete an MRI (contraindications for MRI) * Known presence of other neurologic disorders * Known active infection or history of or presence of recurrent or chronic infection * History of cancer, including solid tumors and hematological malignancies (except for basal cell, in situ squamous cell carcinomas of the skin and in situ carcinoma of the cervix that have been excised and resolved) * Previous treatment with B-cell targeted therapies (e.g. rituximab, ocrelizumab, atacicept, belimumab, or ofatumumab) * Any previous treatment with lymphocyte trafficking blockers, with alemtuzumab, anti-cluster of differentiation 4 (CD4), cladribine, cyclophosphamide, mitoxantrone, azathioprine, mycophenolate mofetil, cyclosporine, methotrexate, total body irradiation, or bone marrow transplantation * Any concomitant disease that may require chronic treatment with systemic corticosteroids or immunosuppressants during the course of the study