At-Risk for Type 1 Diabetes Extension Study

Inclusion Criteria:

1. Previous participant in the TN-10 study
2. Participant has received a diagnosis of type 1 diabetes after the conclusion of the TN-10 study, according to the criteria from the American Diabetes Association (ADA).
3. Participant is able to initiate teplizumab treatment required in this study within 1 year of type 1 diabetes diagnosis.
4. Participant is willing to forego other forms of experimental treatment during the entire study.
5. Participant and/or guardian has given informed consent and assent as applicable.

Exclusion Criteria:

1. Has an active infection and/or fever.
2. Has a history of or serologic evidence at screening of current or past infection with human immunodeficiency virus (HIV), hepatitis B virus (HBV), or hepatitis C virus (HCV).
3. An individual who has a medical, psychological or social condition that, in the opinion of the Principal Investigator, would interfere with safe and proper completion of the trial.