This is a multicenter, randomized, double-blind, parallel, placebo-controlled, Phase 3, 2-arm study. The purpose of this study is to evaluate safety and efficacy of teplizumab, by assessing glycated hemoglobin A1c (HbA1c) change, and the total number of days without prandial insulin use, from baseline to Week 52, with teplizumab compared with placebo, both administered by intravenous (IV) infusion, in participants with recently diagnosed Stage 3 T1D aged 1 to 25 years, on standard insulin therapy.

Who can Participate

Stage 3 T1D within 6 weeks of diagnosis Ages 1-25 I 01. Participant must be 1 to 25 years of age inclusive, at the time of signing the informed consent. I 02. Participants diagnosed with T1D Stage 3 according to American Diabetes Association 2025 criteria (9). I 03. Participants able to be randomized and initiate study drug within 8 weeks (56 days) of the Stage 3 T1D diagnosis (the 8 weeks may be extended to within 12 weeks of diagnosis in case a mandatory live vaccine must be administered) I 04. Participants must be positive for at least one T1D autoantibody at screening: a) Glutamic acid decarboxylase (GAD-65), b) Insulinoma Antigen-2 (IA-2), c) Zinc-transporter 8 (ZnT8), or d) Insulin (if obtained not later than 14 days after exogenous insulin therapy initiation). e) Islet cell cytoplasmic autoantibodies (ICAs) Note: Documented positive T1D autoantibody(ies) obtained prior to screening are also acceptable. I 05. Have random C-peptide level ≥0.2 nmol/L obtained at screening Note: For children less than 3 years of age, any detectable random C-peptide at screening is acceptable for the inclusion E 01. Participant has diabetes other than autoimmune T1D that includes but is not limited to genetic forms of diabetes, maturity-onset diabetes of the young (MODY), diabetes secondary to medications or surgery and type 2 diabetes by judgement of the Investigator. E 02. Participant has an active serious infection and/or fever ≥38.5°C (101.3°F) within the 48 hours prior to the first dose (except if localized skin infection), or has chronic, recurrent or opportunistic infectious disease. E 03. At screening, participant has laboratory or clinical evidence of acute or clinically active infection with Epstein-Barr virus (EBV), cytomegalovirus (CMV). E 04. At screening, participant has positive serology for human immunodeficiency virus (HIV), hepatitis B (HBV), or hepatitis C (HCV). E 05. Participant has evidence of active or latent tuberculosis (TB) as documented by medical history and examination, chest X-rays (posterior anterior and lateral), and/or TB testing. Blood testing (eg, QuantiFERON® TB Gold test) is strongly preferred; if not available, any local approved TB test is allowed. E 06. Has other autoimmune diseases, (eg, rheumatoid arthritis, polyarticular juvenile idiopathic arthritis, psoriatic arthritis, ankylosing spondylitis, multiple sclerosis, systemic lupus erythematosus etc), except clinically stable autoimmune thyroid disease, or controlled celiac disease (at discretion of Investigator). E 07. Any clinically significant abnormality identified either in medical/surgical history or during screening evaluation (eg, physical examination, laboratory tests, vital signs), or any AE during screening period which, in the judgment of the Investigator, would preclude safe completion of the study or constrains efficacy assessment.

Study ID