Project Summary The overall objective of the work supported by this grant has been to develop therapies to treat, delay, or prevent Type 1 diabetes (T1D). The work from prior funding cycles has changed the field. The studies have included clinical and mechanistic investigations that led to the first drug approved by the FDA for delay of T1D (or any autoimmune disease), and the only drug approved to change the course of T1D since the discovery of insulin, more than 100 years ago. Our studies have led to the understanding that teplizumab modifies CD8+ T cells and induces a signal that leads to partial exhaustion, effects of drug treatment on β cells, and patient features that can affect these responses. However, a number of new questions have emerged which are essential to address to further advance immune therapy for T1D with teplizumab or other agents. The phenotypes of CD8+ T cells that identify responses to the drug diminish by 18 months after drug treatment indicating that there are other factors that account for the long term responses that are seen in some patients. In addition, not all patients respond but the features of responders and the mechanisms that sustain the clinical benefits are not well understood. In this continuation proposal we aim to test two hypotheses related to the mechanisms of teplizumab in clinical responders. We will use unique clinical samples from two successful clinical trials to address these hypotheses – from the TN10 teplizumab prevention trial (a Phase II trial testing whether teplizumab would delay the time to diagnosis of Stage 3 clinical T1D in patients at risk with Stage 2 disease) including samples from patients who have shown clinical responses for more than 10 years from a course of drug, and the PROTECT trial, a Phase III clinical trial of patients with new onset T1D. In the first aim we will test the hypothesis that teplizumab induces specific changes in autoantigen reactive T cells that results in its efficacy. We will compare the transcriptome. phenotype (with CITEseq), and epigenome (with ASAP-seq) of auto and viral antigen specific CD8+ T cells in samples from responders and non-responders from the two clinical trials including samples from patients whose duration of response is more than 10 years. In the second aim, we will test the hypothesis that the host environment, which may be shaped by prior infection (with EBV), commensals (identified by anti-commensal antibodies), age, HLA type, and other factors, determines responses to teplizumab treatment in responders and non-responders. We will use single cell techniques to evaluate cells from the patients in the two clinical trials. We will use this information to develop a model that incorporates the single cell and clinical features to predict clinical responses to teplizumab. These studies will identify immune mechanisms that can lead to operational tolerance. This information is important for understanding the pathogenesis of human T1D. I enable...