After joining the study, treatment will begin within 8 weeks (56 days) of receiving the diagnosis of Type 1 Diabetes.

Treatment will be assigned randomly, meaning it will be determined by chance. This is a double-blind study, which means neither the participant nor the medical team will know whether teplizumab or placebo (an inactive substance with no medication) is being administered.

Teplizumab is administered as an intravenous infusion, which means the medication is delivered directly into a vein through a drip. The placebo is administered in the same manner.

The medication is provided as a concentrate for solution for infusion, which is prepared before administration.

The assigned treatment (either teplizumab or placebo) will be administered through intravenous infusion.

The infusions will be given according to a specific schedule determined by the study protocol.

During each infusion visit, vital signs and any reactions to the treatment will be monitored.

The main study period lasts 52 weeks (approximately one year).

During this time, multiple assessments will be conducted to evaluate how well blood sugar levels are controlled.

Regular measurements of HbA1c (glycated hemoglobin) will be taken. This is a blood test that shows the average blood sugar level over the past 2 to 3 months.

The amount of insulin needed for meals (called prandial insulin) will be tracked. The study will monitor how many days the participant can manage without needing insulin at mealtimes.

C-peptide levels will be measured. C-peptide is a substance produced by the pancreas that indicates how much insulin the body is still able to produce naturally.

A mixed meal tolerance test will be performed. This test involves drinking a standardized meal replacement drink, and then blood samples are taken over a 2-hour period to measure how the body responds.

Continuous glucose monitoring may be used. This involves wearing a small sensor that tracks blood sugar levels throughout the day and night.

The amount of time blood sugar stays within the target range (70-180 mg/dL) will be measured. This is called time-in-range.

Any episodes of hypoglycemia (low blood sugar) will be recorded and classified according to their severity.

All side effects, adverse events, and any serious health problems will be documented throughout the study period.

Throughout the study, safety will be continuously monitored.

Blood samples will be taken to check for antidrug antibodies. These are proteins the immune system might produce in response to the medication.

Blood samples will also be analyzed to measure the concentration of teplizumab in the bloodstream at various time points. This helps determine how the body processes the medication.

Any health changes, side effects, or concerns will be evaluated and recorded.

If serious side effects occur, treatment may need to be stopped.

After completing the 52-week main study period, there will be additional follow-up.

The total study duration extends until approximately December 2028.

Follow-up visits will continue to assess long-term effects and safety.

Diabetes management and insulin requirements will continue to be monitored.

The ability of the pancreas to produce insulin naturally will be assessed through continued C-peptide measurements.

Female participants of childbearing potential must use highly effective contraception (with less than 1% failure rate) during the treatment period and for at least 30 days after the last dose of study medication.

Pregnancy tests will be performed at screening and within 24 hours before the first treatment administration.

If breastfeeding, the participant must stop breastfeeding during treatment and for 20 days after the last dose. Breast milk must be pumped and discarded during this time.