• Primary outcome measures will include the number and percentage of subjects who experience a SAE, Adverse Event of Special Interest (including Opportunistic Infection, Lymphopoliferative disease), or other Immediately Reportable Event. [ Time Frame: Duration of the study- 3 years ] [ Designated as safety issue: Yes ]
  

• A secondary endpoint will be determining the efficacy of teplizumab by measuring the subject's total daily insulin usage and HbA1c levels. [ Time Frame: Month 6, 12, 18, 24, 30, 36 ] [ Designated as safety issue: No ]
  
• C-peptide secretory response will be analyzed in terms of basal levels of C-peptide produced before a mixed meal and stimulated levels after a mixed meal, measured as AUC and peak post-meal production. [ Time Frame: Month 6, 12, 18, 24, 30, 36 ] [ Designated as safety issue: No ]
  
• Immunophenotyping of blood mononuclear cells will be summarized by visit and graphed over time, as appropriate. [ Time Frame: Month 6, 12, 18, 24, 30, 36 ] [ Designated as safety issue: No ]
  
• A secondary efficacy endpoint will be assessing Heath Related Quality of Life Questionnaires filled out by subjects at different timepoints in the study. [ Time Frame: Month 6, 12, 18, 24, 30, 36 ] [ Designated as safety issue: No ]
  

The primary objective of the extension study is to assess long-term safety, with particular focus on the development of serious adverse events (SAEs), adverse events of special interest (AESIs) including opportunistic infections and lymphoproliferative disease, and other immediately reportable events (IREs), in subjects with recent-onset T1DM who complete CP-MGA031-01.

The secondary objectives of the extension study are to: 1) assess long-term efficacy; 2) evaluate immunological effects(North America only); 3) measure anti-teplizumab antibody levels;4) assess Health Related Quality of Life Questionnaires.