A Study to Investigate Efficacy and Safety of Teplizumab Compared With Placebo in Participants 1 to 25 Years of Age With Stage 3 Type 1 Diabetes

Inclusion Criteria: * Participants are eligible to be included in the study only if all of the following criteria apply: * Participant must be 1 to 25 years of age inclusive, at the time of signing the informed consent. * Participants diagnosed with T1D Stage 3 according to American Diabetes Association 2025 criteria * Participants able to be randomized and initiate study drug within 8 weeks (56 days) of the Stage 3 T1D diagnosis * Participants must be positive for at least one T1D autoantibody at screening: * Glutamic acid decarboxylase (GAD-65), * Insulinoma Antigen-2 (IA-2), * Zinc-transporter 8 (ZnT8), or * Insulin (if obtained not later than 14 days after exogenous insulin therapy initiation). * Islet cell cytoplasmic autoantibodies (ICAs) * Have random C-peptide level ≥0.2 nmol/L obtained at screening * Enter Inclusion Criteria Sex * Both male and female participants are eligible. * Contraceptive use by women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies. * A female participant is eligible to participate if she is not pregnant, and one of the following conditions applies: * Is a woman of nonchildbearing potential (WONCBP) OR * Is a woman of…

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