- Participant has any medical or psychiatric condition that, in the opinion of the Investigator, could jeopardize or would compromise the participant’s ability to participate in this study - Participant has a known hypersensitivity to any components of the study medication as stated in this protocol - Participant has had a thymectomy within 6 months prior to Baseline or has one scheduled to occur during the 12-week Main Treatment Period - Participant has a history of meningococcal disease - Participant has or has had a current or recent systemic infection within 2 weeks prior to Baseline or an infection requiring IV antibiotics within 4 weeks prior to Baseline - Participant has active malignancy (except curatively resected squamous or basal cell carcinoma of the skin) requiring surgery, chemotherapy, or radiation within the prior 12 months (participants with a history of malignancy who have undergone curative resection or otherwise not requiring treatment for at least 12 months prior to Screening with no detectable recurrence are allowed). - Participant has a lifetime history of suicide attempt (including an actual attempt, interrupted attempt, or aborted attempt), or has had suicidal ideation with at least some intent to act in the past 6 months as indicated by a positive response (“Yes”) to either question 4 or question 5 of the “Screening/Baseline” version of the C-SSRS at Screening. - Participant has alanine transaminase (ALT), aspartate aminotransferase (AST), or alkaline phosphatase (ALP) >2.5x upper limit of normal (ULN) - Participant has bilirubin >1.5xULN (isolated bilirubin >1.5xULN is acceptable if bilirubin is fractionated and direct bilirubin <35%). - Participant has current unstable liver or biliary disease per Investigator assessment defined by the presence of ascites, encephalopathy, coagulopathy, hypoalbuminemia, esophageal or gastric varices, persistent jaundice, or cirrhosis. - QTc interval >450msec for male participants, QTc >470msec for female participants, or QTc >480 msec in participants with bundle branch block - Participant has had recent surgery requiring general anesthesia within 2 weeks prior to Screening or is expected to have surgery requiring general anesthesia during the 12-week Main Treatment Period - Participant has received a treatment with an experimental drug within 30 days or 5 half lives of the experimental drug (whichever is longer) prior to Baseline - Participant has received treatment with rituximab within 6 months prior to Baseline or treatment is planned to occur during the study - Participant has received treatment with intravenous immunoglobulin G (IVIG), SC immunoglobulin, or plasma exchange PLEX 4 weeks prior to Baseline or participant is on chronic IVIG, SC immunoglobulin, or PLEX - Participant has previously participated in this study or participant has previously been assigned to treatment in a study of the medication under investigation in this study - Participant has participated in another study of an investigational study medication (and/or an investigational device) within the previous 30 days or is currently participating in another study of an investigational study medication (and/or an investigational device) - Participant has known positive serology for muscle-specific kinase