A Study to Investigate the Safety, Tolerability, and Processing by the Body of Intravenous and Subcutaneous RO7121932 Administration in Participants With Multiple Sclerosis

Primary: Parts 1, 2, and 3: Change From Baseline in Suicide Risk as Assessed Using the Columbia-Suicide Severity Rating Scale (C-SSRS), Parts 1, 2, and 3: Percentage of Participants With Adverse Events (AEs) and Serious Adverse Events (SAEs) With Severity of AEs Measured According to National Cancer Institute Common Terminology Criteria for Adverse Events Version 5 (NCI CTCAE V5), Parts 2 and 3: Percentage of Participants With Local Injection-site Reaction Using Local Injection-site Symptom Assessment (LISSA), Parts 2 and 3: Percentage of Participants With Local Pain at the Site of Injection Assessed Using the Visual Analog Scale (VAS)

Secondary: Part 1: Total Body Clearance (CL) Of RO7121932, Parts 1 and 2: AUC From Time 0 to Infinity (AUCinf), Parts 1 and 3: Change From Baseline in B-cell Frequencies in CSF, Parts 1, 2 and 3 (Week 1 and Week 4): Maximum Observed Serum Concentration (Cmax) of RO7121932, Parts 1, 2 and 3 (Week 1 and Week 4): Time to Maximum Observed Concentration (Tmax) of RO7121932, Parts 1, 2 and 3: Apparent Terminal Half-Life (T1/2) of RO7121932, Parts 1, 2, and 3: Change From Baseline in B-cell Frequencies in Blood, Parts 2 and 3 (Week 4): Apparent Clearance (CL/F) of RO7121932