Platform Trial to Delay Stage 3 Diabetes: Comparing Teplizumab With ATG

This protocol will enroll 60 participants between the ages of 4 and 34 with Stage 2 Type 1 diabetes. Oral glucose tolerance testing will be done at the screening, baseline visit (V0) and at 3, 6 and 12 months in the first year after study drug administration. Eligible study participants will be randomized to recieve either 2 doses of ATG over 2-3 days or 14 doses of teplizumab given once daily over 14 consecutive days. Safety labs will also be done during select study visits to monitor the participant's health. Once the treatment phase has been completed, participants will have 3 in-person study visits in year one of the study with interim contact to assess adverse events and symptoms of diabetes. After year one of the study, participants will continue in-person follow-up visits every 6 months until the last enrolled participant completes the 12-month visit or develops Stage 3 Type 1 diabetes, whichever occurs first. The total initial study duration is expected to last 3-4 years. There is a possibility the study will be extended after the initial study duration, dependent upon the primary outcome (DPTRS at the month 6 visit) and as determined by TrialNet. If the study extension is done, participants would be presented an additional consent form to opt into additional follow-up visits which would increase total time in study to about 9 years.