Inclusion Criteria:

1. Previous participant in the TN-10 study
2. Participant had 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 was able to initiate teplizumab treatment required in this study within 1 year of type 1 diabetes diagnosis.
4. Participant was willing to forego other forms of experimental treatment during the entire study.
5. Participant and/or guardian had given informed consent and assent as applicable.

Exclusion Criteria:

1. Had an active infection and/or fever.
2. Had 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 had a medical, psychological or social condition that, in the opinion of the Principal Investigator, would interfere with safe and proper completion of the trial.