The purpose of this study is to determine whether teplizumab slows the loss of β cells and preserves β cell function in children and adolescent 8-17 years old who have been diagnosed with T1D in the previous 6 weeks.. Subjects will receive two courses of either teplizumab or placebo treatment 6 months apart.

This is a Phase 3, randomized, double-blind, placebo-controlled, multinational, multi-center study to evaluate the efficacy and safety of teplizumab, a humanized, anti-CD3 monoclonal antibody, in children and adolescents ages 8 through 17 recently diagnosed with type 1 diabetes (within 6 weeks of diagnosis). Approximately 300 participants will be randomized at a ratio of 2:1 to either the teplizumab group or the placebo group. Teplizumab or matching placebo will be administered in two courses 6 months apart. Each course of treatment will include daily infusions for 12 days. The total study duration for each participant will be up to 86 weeks. The primary objective is to determine whether two courses of teplizumab administered 6 months apart slows the loss of β cells and preserves β cell function over 18 months (78 weeks) in children and adolescents 8-17 years old who have been diagnosed with T1D in the previous 6 weeks. The secondary objectives are to evaluate improvements in key clinical parameters of diabetes management, to determine the safety and tolerability of teplizumab, and to evaluate the pharmacokinetics (PK) and immunogenicity of teplizumab