The area under the concentration-time curve (AUC) of C-peptide was measured after a 4-hour mixed meal tolerance test (MMTT) and is a measure of endogenous insulin production and β cell function. The AUC was computed using the trapezoidal rule and standardized by the duration of the MMTT test, i.e., AUC was divided by the last blood sample collection time (240 minutes or the last collection time for 4h MMTT).

Intent-to-treat (ITT) and Per Protocol (PP). The main reason participants were excluded from the PP population was for treatment compliance <80% (15 of 16 excluded participants in the placebo group and 32 of 37 in the teplizumab group). Other reasons included took prohibited medication (1 in placebo group, 3 in teplizumab group), received incorrect treatment (2 in teplizumab group), and pregnancy (1 in teplizumab group).

The average daily insulin use was calculated based on participants who have at least 3 days of insulin use recorded in the dairy for the Week 78 visit.

Intent-to-treat and Per Protocol

Change in percentage (%) glycated hemoglobin (HbA1c)

Intent-to-treat and Per Protocol

Time in range (%) for glycemia control was assessed using Continuous Glucose Monitoring (CGM). Time in range was defined as daily average percentage of time a participant's glucose is >= 70 mg/dL and <=180 mg/dL. Time in range was calculated based on participants who had at least 3 days of CGM data recorded for Week 78 visit with a range of at least 8 hours on a given day.

Intent-to-treat and Per Protocol

Rate = clinically important hypoglycemic events/patient-year. A clinically important episode was defined as a blood glucose value of <54 mg/dL (3.0 mmol/L) (i.e., Level 2 Hypoglycemia, International Hypoglycemia Study Group, 2017) or a hypoglycemia event of severe cognitive impairment requiring external assistance (such as seizure, syncope, severe confusion with or without a confirmatory low blood glucose reading) (i.e., Level 3 Hypoglycemia, International Hypoglycemia Study Group 2017). Event rate was calculated for each participant as number of events / total study follow-up time. Total study follow-up time was calculated as (the date of last study contact - the first dose date + 1)/365.25. The summary is based on the data reported post-baseline in the Hypoglycemic Events Electronic Diary (eDiary).

Intent-to-treat and Per Protocol

AESIs are defined in the protocol and categories in the statistical analysis plan. Participants with multiple events are counted only once for each preferred term and category.

Safety population = all randomized study participants receiving any exposure to study drug.

PK samples were collected prior to dosing except for Day 9 in Course 1. An additional PK sample was collected 45 minutes after infusion on Day 9 in Course 1. Concentration values below Lower Limit of Quantification (2.50 ng/mL) were set to zero for summary statistics. Course 2 day numbers were set relative to the first day of dosing, regardless of normal or modified dosing schedule.

The Pharmacokinetic (PK) population includes all randomized participants who received at least one dose of teplizumab with at least one valid pharmacokinetic sample.

Baseline was defined as the most recent value collected prior to the first dose of study drug. Week 26 Day 187 and Weeks 27 and 34 are planned for subjects under the normal dosing schedule. Week 52 Day 369 and Weeks 53, 56, and 60 are planned for subjects under the modified dosing schedule.

The Immunogenicity population includes all randomized participants who received at least one dose of teplizumab with at least one valid serum Anti-teplizumab Antibody (ADA) sample.

Baseline is defined as the most recent value collected prior to the first dose of study drug. Week 26 Day 187 and Weeks 27 and 34 are planned for subjects under the normal dosing schedule. Week 52 Day 369 and Weeks 53, 56, and 60 are planned for subjects under the modified dosing schedule.

The Immunogenicity population includes all randomized participants who received at least one dose of teplizumab with at least one valid serum Anti-teplizumab Antibody (ADA) sample.