The goal of this Phase 2 study is to assess safety and efficacy of frexalimab to preserve -cell function in participants with newly diagnosed type 1 diabetes (T1D). In Part A, an exploratory part, adults (ages 18-35) will be treated with either high dose frexalimab, or placebo (inactive study drug). In Part B, adolescents and young adults (ages 12-21) will be treated with 3 dose levels of frexalimab or placebo.

This study wants to know about the problems that Black or African American teenagers with type 1 diabetes (T1D) and their families face. It also wants to see how these problems affect their feelings, behavior, and how they get along with others. The study will find out how well they can handle T1D and adapt to it. It will also learn how good things like being strong, family, and where they live might help young people who have to deal with hard things. This includes how well they handle their feelings, behavior, relationships, and T1D care.