The goal of this study is to determine how a drug class called glucagon-like peptide-1 receptor agonists (GLP-1Ra) affects people during an early stage of Type 1 Diabetes undergoing clinical teplizumab treatment. This study involves giving participants a liquid meal under different conditions and observing how their bodies respond, focusing on blood sugar levels, insulin effectiveness, and blood vessel function. The meal tests are followed by two post-treatment tests, one with the GLP-1Ra drug and the other with a placebo. Each test involves blood draws before and during the meal test, GLP-1Ra or placebo administration, and an ultrasound to measure blood vessel function. The goal is to see if GLP-1Ra can help manage blood sugar levels and improve cardiovascular health in this population.

The long-term goal is to determine whether repurposing GLP-1Ra for stage 2 in combination with immunotherapy can modify the disease course, reducing the need for exogenous insulin therapy and leading to improved cardiometabolic outcomes and quality of life. For early stage 3 T1DM, we aim to determine whether GLP-1Ra can offer similar protective effects in preserving β-cell function and stabilizing glycemic control. The immediate objective is to investigate the impact of GLP-1Ra's insulinotropic and glucagonostatic effects on dysmetabolism in stage 2 and early stage 3 T1DM. The study hypothesizes that these effects will each delay the need for exogenous insulin by improving three key aspects of dysmetabolism: 1) postprandial glycemia, 2) disposition index (i.e., the ability of the islet cells to compensate for a given insulin sensitivity), and 3) endothelial function. The rationale for this hypothesis is based on two observations: first, GLP-1Ra combined with immunomodulatory therapy sustains endogenous secretion in response to a mixed meal tolerance test (MMTT) during the first year of stage 3; and second, GLP-1Ras mitigate postprandial hyperglucagonemia in longer-duration T1DM. To test the hypothesis, studies will be conduct in individuals with stage 2 T1DM treated with teplizumab using a crossover design structured around the following specific aims: Aim 1: Investigate the impact of GLP-1Ra on postprandial glycemia in a pilot study. The study team will measure postprandial glycemia during an MMTT before teplizumab treatment. After teplizumab the study team will compare the effects of placebo versus semaglutide (a GLP-1Ra). Aim 2: Study the impact of GLP-1Ra on the disposition index (DI) in a pilot study. The study team will use the oral glucose minimal model to measure DI during an MMTT before and after teplizumab treatment, comparing the effects of placebo versus semaglutide. As an exploratory outcome, β-cell endoplasmic reticulum dysfunction will be quantified by measuring the proinsulin-to-C-peptide ratio during the MMTT. Aim 3: Determine the impact of GLP-1Ra on endothelial function in a pilot study. The study team will use B-mode ultrasound to measure flow mediated vasodilation (FMD), a bioassay of endothelial function, during each MMTT. Because endothelial cells are often among the first affected by hyperglycemia and insulin resistance, the study aims to illuminate how GLP-1Ra may mitigate early vascular disease progression. And in a pilot study of early stage 3 T1DM, 4) GLP-1 Receptor Agonists. Aim 4: Determine how much GLP-1Ra monotherapy therapy changes the disposition index (DI) in a pilot study of early stage 3 T1DM. Despite the promise of TZIELD®, the medication is not currently approved for patients with stage 3 T1DM. Thus, individuals who progress into stage 3 T1DM continue to face significant challenges, including loss of β-cell function and the need for exogenous insulin. As patients move into stage 3, there is an opportunity for metabolic interventions that may preserve residual insulin production and mitigate the long-term impact of hyperglycemia. Accordingly, we will conduct a randomized, double-blind, placebo-controlled crossover study involving patients with early stage 3 T1DM. Each participant will undergo four mixed meal tolerance tests (MMTTs): two at baseline shortly after diagnosis and two after a six-month interval. During each MMTT, participants will receive either a single dose of GLP-1Ra (oral semaglutide) or placebo in a randomized order. This design allows us to assess the independent effects of GLP-1Ra on the disposition index (DI) by comparing the results between the GLP-1Ra and placebo conditions at both time points. By evaluating changes in DI and other metabolic parameters over time, we aim to determine how GLP-1Ra monotherapy influences β-cell function and insulin sensitivity in early stage 3 T1DM.