A PHASE III, RANDOMIZED, DOUBLE-BLIND, PLACEBO-CONTROLLED, MULTICENTER BASKET STUDY TO EVALUATE THE EFFICACY, SAFETY, PHARMACOKINETICS, AND PHARMACODYNAMICS OF SATRALIZUMAB IN PATIENTS WITH ANTI-N-METHYL-D-ASPARTIC ACID RECEPTOR (NMDAR) OR ANTI-LEUCINE…

Inclusion Criteria:
*  Reasonable exclusion of tumor or malignancy before baseline visit (randomization)
*  Onset of autoimmune encephalitis (AIE) symptoms \<=9 months before randomization
*  Meet the definition of "New Onset" or "Incomplete Responder" AIE
*  For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use adequate contraception during the treatment period and for at least 3 months after the final dose of satralizumab or placebo
*  For participants enrolled in the extended China enrollment phase at National Medical Products Administration (NMPA)-recognized sites: participants who are current residents of mainland China, Hong Kong, or Taiwan, and of Chinese ancestry N-methyl-D-aspartic acid receptor (NMDAR) AIE Cohort
*  Age \>=12 years
*  Diagnosis of probable or definite NMDAR encephalitis Leucine-rich glioma-inactivated 1 (LGI1) AIE Cohort
*  Age \>=18 years
*  Diagnosis of LGI1 encephalitis

Exclusion Criteria:
*  Any untreated teratoma or thymoma at baseline visit (randomization)
*  History of carcinoma or malignancy, unless deemed cured by adequate treatment with no evidence of recurrence for \>=5 years before screening
*  For patients with NMDAR AIE, history of negative anti-NMDAR antibody in cerebrospinal fluid (CSF) using a cell-based assay within 9 months of symptom onset
*  Historically known positivity to an intracellular antigen with high cancer association or GAD-65
*  Historically known positivity to any cell surface neuronal antibodies other than NMDAR and LGI1
*  Confirmed paraneoplastic encephalitis
*  Confirmed central or peripheral nervous system demyelinating disease
*  Alternative causes of associated symptoms
*  History of herpes simplex virus encephalitis in the previous 24 weeks
*  Any previous/concurrent treatment with IL-6 inhibitory therapy (e.g., tocilizumab), alemtuzumab, total body irradiation, or bone marrow transplantation
*  Any previous treatment with anti-CD19 antibody, complement inhibitors, neonatal Fc receptor antagonists, anti-B-lymphocyte stimulator monoclonal antibody
*  Any previous treatment with T-cell depleting therapies, cladribine, or mitoxantrone
*  Treatment with oral cyclophosphamide within 1 year prior to baseline Treatment with any investigational drug (including bortezomib) within 24 weeks prior to screening
*  Concurrent use of more than one IST as background therapy
*  Contraindication to all of the following rescue treatments: rituximab, IVIG, high-dose corticosteroids, or intravenous (IV) cyclophosphamide
*  Any surgical procedure, except laparoscopic surgery or minor surgeries within 4 weeks prior to baseline, excluding surgery for thymoma or teratoma removal
*  Planned surgical procedure during the study
*  Evidence of progressive multifocal leukoencephalopathy
*  Evidence of serious uncontrolled concomitant diseases that may preclude patient participation
*  Congenital or acquired immunodeficiency, including HIV infection
*  Active or presence of recurrent bacterial, viral, fungal, mycobacterial infection, or other infection
*  Infection requiring hospitalization or treatment with IV anti-infective agents within 4 weeks prior to baseline visit
*  Positive hepatitis B (HBV) and hepatitis C (HCV) test at screening
*  Evidence of latent or active tuberculosis (TB)
*  History of drug or alcohol abuse within 1 year prior to baseline
*  History of diverticulitis or concurrent severe gastrointestinal (GI) disorders that, in the investigator's opinion, may lead to increased risk of complications such as GI perforation
*  Receipt of live or live-attenuated vaccine within 6 weeks prior to baseline visit
*  History of blood donation (1 unit or more), plasma donation or platelet donation within 90 days prior to screening
*  History of severe allergic reaction to a biologic agent
*  Active suicidal ideation within 6 months prior to screening, or history of suicide attempt within 3 years prior to screening
*  Any serious medical condition or abnormality in clinical laboratory tests that, in the investigator's judgment, precludes safe participation in and completion of the study
*  Pregnant or breastfeeding, or intending to become pregnant during the study or within 3 months after the final dose of study drug
*  Laboratory abnormalities at Screening