A Trial of Inebilizumab in Participants With Autoimmune Hepatitis

Inclusion Criteria: * Signed informed consent. * Age ≥ 18 years or legal adult age within the country, whichever is older and \< 75 years at the time of signing the informed consent. * Participants must have either inadequate response to at least 9 months of SOC or are intolerant to SOC within 6 months of screening. Inadequate response to SOC treatment is defined as ALT ≥ 2 upper limit of normal (ULN) at screening after at least 9 months of SOC, including prednisone (or equivalent) \> 5 mg/day and at least one conventional steroid sparing agent at guideline-concordant target or highest appropriate dose, that is azathioprine (AZA) or 6-mercaptopurine (6-MP) at appropriate weight-based dosing (typically up to 2 mg/kg/day AZA or 1 mg/kg/day 6-MP) or mycophenolate (MMF) up to 2 g/day, as judged appropriate by the investigator and documented in the medical record. Intolerance to SOC treatment is defined as any clinically significant adverse event related to treatment that results in discontinuation of the medication or prevents dose optimization necessary to achieve or maintain biochemical response, as determined by the Principal Investigator (PI). Intolerance applies to GCs, AZA, 6-MP, or MMF. Presence of one or more clinically significant adverse effects attributed to SOC include but not limited to side effects that, in the opinion of the investigator, compromise participant's safety or quality of life, exacerbate comorbid conditions, or render continued use medically inappropriate. * Participants with disease activity at screening as follows: ALT ≥ 2 x ULN to ≤ 7 x ULN. ALT ULN values will be gender specific. * Participant must have a biopsy proven definitive diagnosis of AIH according to simplified diagnostic criteria (score ≥ 7). Liver biopsy should be obtained within 90 days prior to randomization. Participants must have a mHAI score ≥ 5 in the biopsy. * Participant should be on: * No increase in GC dose during the 28 days immediately preceding whichever biopsy is designated as the baseline sample-historical or screening-and the dose post biopsy must remain unchanged through the day of randomization AND * Stable maximum tolerated doses of AZA or 6-MP for at least 12 weeks prior to screening (baseline) liver biopsy until randomization and during the entire treatment period unless dose reduction is deemed necessary for safety or tolerance reasons OR * Stable maximum tolerated doses of MMF/mycophenolic acid (MPA) for at least 12 weeks prior to screening (baseline) liver biopsy until randomization and during the entire treatment period unless dose reduction is deemed necessary for safety or tolerance reasons. * Participants must use protocol-specified contraception during treatment and for an additional 6 months after the last dose of trial intervention. Exclusion Criteria: * Diagnosis of definitive overlap autoimmune liver or rheumatologic syndrome with autoimmune hepatitis (eg, AIH + primary biliary cholangitis \[PBC\], AIH + primary sclerosing cholangitis \[PSC\], AIH related to Systemic Lupus Erythematosus, etc) where established overlap criteria are met. * Acute liver failure (ALF) at screening (e.g., acute hepatic dysfunction with coagulopathy and any degree of encephalopathy) in the investigator's judgment. * Participant has known history of: * Allergy or reaction to any component of inebilizumab formulation or history of anaphylaxis to any human gamma globulin therapy. * Allergy to or intolerance of protocol-required treatment, including medications for prophylaxis of infusion reactions (antipyretic such as paracetamol/acetaminophen or equivalent, diphenhydramine or equivalent, and methylprednisolone or equivalent). * Active malignancy or history of malignancy that was active within the last 10 years, except as follows: * In situ carcinoma of the cervix treated with apparent success with curative therapy for \> 12 months prior to screening * Curatively treated breast ductal carcinoma in situ * Cutaneous basal cell or squamous cell carcinoma treated with apparent success with curative therapy for \> 12 months prior to screening * Prostate cancer treated with radical prostatectomy or radiation therapy with curative intent \> 3 years prior to screening and without known recurrence or current treatment * Thyroid cancer for which complete surgical resection has been performed within 5 years with well-differentiated histology (papillary thyroid carcinoma or follicular thyroid carcinoma) and there is no evidence of active disease. * Known positive test for human immunodeficiency virus (HIV) infection. Evidence of HIV infection or positive for HIV antibodies at initial screening or current acquired, common variable or inherited, primary or secondary immunodeficiency. * Presence or history of viral hepatitis infection: * Positive test for, or prior treatment for, hepatitis B. A positive test for hepatitis B is detection of either: * Positive for hepatitis B surface antigen (HBsAg) OR * anti-HBc * Participants with a history of or current hepatitis C virus (HCV) infection, even those considered to be cured. * Active tuberculosis (TB) or latent TB with no documented history of adequate treatment per local SOC. * Positive test for TB during screening is defined as positive QuantiFERON® test. At screening, all participants must be tested with an interferon-γ release assay (IGRA) (QuantiFERON®). * History of \> 1 episode of herpes zoster (any grade) and/or any other definite or probable opportunistic infection in the 12 months prior to screening. * Estimated glomerular filtration rate \< 45 mL/min/1.73 m\^2 using chronic kidney disease epidemiology (CKD-EPI) 2021 formula. * Blood tests at screening that meet any of the following criteria: * Hemoglobin \< 7.5 g/dL * Neutrophils \< 1200/mm\^3 * Platelets \< 150 x 10\^9/L * international normalized ratio (INR) \> 1.3 * cluster of differentiation 19 (CD19)+ B cells at screen \< 40 cells/µL; an excl