Anti-CD3 monoclonal antibody (a.k.a. hOKT3gamma1 [Ala-Ala],teplizumab, MGA031) is a humanized antibody that is commonly used to prevent organ rejection. The purpose of this study is determine whether anti-CD3 mAb treatment can halt the progression of newly diagnosed type 1 diabetes.

Type 1 diabetes is an autoimmune disease in which the immune system mistakenly attacks insulin-producing beta cells in the pancreas. Without these cells, the body cannot maintain proper blood glucose levels in response to daily activities, such as eating or exercise. Generally, at the time of type 1 diabetes diagnosis, 60% to 85% of the diabetic person's beta cells have already been destroyed. However, between 15% and 40% of these cells remain and are able to produce insulin. Treatment that slows the destruction of additional beta cells may be able to decrease a patient's reliance on insulin and improve their quality of life.

Anti-CD3 mAb is genetically engineered and directed against the CD3 antigen on T cells; this antibody selectively attacks the immune cells responsible for beta cell destruction. In a small exploratory clinical trial, patients with newly diagnosed type 1 diabetes who received a single, 2-week treatment with anti-CD3 mAb had preserved beta cell function and significantly lower insulin requirements than untreated patients for up to two years after therapy. This study will investigate whether a second course of anti-CD3 mAb administered one year after the first administration is able to prolong or improve the effects of the biologic in people who have recently diagnosed type 1 diabetes mellitus.

Participants will be randomly assigned to one of two groups. The Experimental Group will receive anti-CD3 mAb treatment plus Diabetes Standard of Care Treatment; the Active Comparator Group will receive Diabetes Standard of Care Treatment. The Experimental Group will be treated with the antibody for the first 14 days of the study and again one year later. These participants will be admitted to the hospital for the first 5 days of a treatment cycle. Participants who live within 1 hour of the hospital may receive the remainder of a treatment cycle as an outpatient, but those who live farther away will be hospitalized for 14 days. For the first treatment cycle, there will be study visits on the 3 consecutive days after the treatment cycle and at Months 1, 2, 3, 6, 9, and 12. For the second treatment cycle, there will be study visits on the 3 consecutive days after the treatment cycle and at Months 13, 16, 19, 21, and 24.The Active Comparator Group will have 12 study visits over two years.

At study entry, all participants will receive daily iron supplementation, either as ferrous sulfate or a multivitamin with iron. Participants will be followed for up to 2 years to assess their overall diabetes health and to capture laboratory measures of beta cell and immune system function. Medication history and adverse event assessment will occur at all visits. A physical exam, vital signs measurement, and blood collection will occur at most visits. Medical history and urine collection will occur at selected visits.

Inclusion Criteria:

• Diagnosis of type 1 diabetes (according to American Diabetes Association [ADA] criteria) within the 8 weeks prior to study entry
• Weigh at least 25 kg (55 lbs)
• Insulin autoantibodies assessed within 10 days of any insulin use OR anti-glutamic acid decarboxylase (GAD) autoantibodies OR anti-ICA512/IA-2 autoantibodies
• Subjects or guardian(s) willing to provide informed consent

Exclusion Criteria:

• Prior participation in a clinical trial that could potentially affect diabetes condition or immunologic status
• Participation in another investigational clinical trial within the 6 weeks prior to study entry
• Pregnancy or breastfeeding

Participant level data and additional relevant materials are available to the public in: 1.) the Immunology Database and Analysis Portal (ImmPort), a long-term archive of clinical and mechanistic data from Division of Allergy, Immunology, and Transplantation (DAIT)-funded grants and contracts that also provides data analysis tools available to researchers; and 2.) TrialShare, the Immune Tolerance Network (ITN) Clinical Trials Research Portal that makes data from the consortium's clinical trials publicly available.

The staff at Northwest Lipid Research Laboratory were masked to the treatment assignment since they performed the mixed-meal tolerance test (MMTT) and the HgA1C assays. All study staff including the PI were masked to the results of the MMTT. They were notified of a detectable or undetectable fasting C-peptide result to assess for continuation to the next treatment cycle.