Ocrelizumab will be administered per schedule as specified in the arms.

Placebo will be administered per schedule as specified in the arms.

The time taken to walk 25 feet, typically measured in seconds. The longer it takes to walk, higher the score, which indicates deterioration and greater impairment. Lower times indicate better performance and greater mobility. Lower the mean change in the score over time, the better performance.

The time taken to walk 25 feet, typically measured in seconds. The longer it takes to walk, higher the score, which indicates deterioration and greater impairment. Lower times indicate better performance and greater mobility. Lower the mean change in the score over time, the better performance.

Participants are instructed to place pegs one by one into each of nine holes arranged in a board stabilized with a plastic nonslip sheet on a solid table, and then to remove these pegs from the holes. Both the dominant and non-dominant hands are tested twice (two consecutive trials for each hand). The participants are required to complete two successful trials for each hand. The amount of time (in seconds) required to place and remove all nine pegs is recorded for each trial. More time = higher raw scores, which indicates deterioration. The lower mean change in the score over time, the better the performance.

Participants are instructed to place pegs one by one into each of nine holes arranged in a board stabilized with a plastic nonslip sheet on a solid table, and then to remove these pegs from the holes. Both the dominant and non-dominant hands are tested twice (two consecutive trials for each hand). The participants are required to complete two successful trials for each hand. The amount of time (in seconds) required to place and remove all nine pegs is recorded for each trial. More time = higher raw scores, which indicates deterioration. The lower mean change in the score over time, the better the performance.

C-SSRS is an assessment tool used to assess lifetime suicidality of participant (at baseline) as well as any new instances of suicidality (C-SSRS since last visit). Structured interview prompts recollection of suicidal ideation, including intensity of ideation, behavior, and attempts with actual/potential lethality. Categories have binary responses (yes/no) and include Wish to be Dead; Non-specific Active Suicidal Thoughts; Active Suicidal Ideation with Any Methods (Not Plan) without Intent to Act; Active Suicidal Ideation with Some Intent to Act, without Specific Plan; Active Suicidal Ideation with Specific Plan and Intent, Preparatory Acts and Behavior; Aborted Attempt; Interrupted Attempt; Actual Attempt (non-fatal); Completed Suicide. Suicidal ideation/behavior is indicated by a "yes" answer to any of the listed categories. Score of 0 is assigned if no suicide risk is present. Score of 1 or higher indicate suicidal ideation or behavior.