DPP4 and type 1 diabetes mellitus: Another avenue of research in T1D is the repurposing of already-approved medications, particularly those that have shown promise in preserving β-cell function in pre-clinical studies, including gastrin, dipeptidyl peptidase-4 inhibitors (DPP-4i), glucagon-like peptide 1 receptor agonists (GLP-1RA), γ-aminobutyric acid (GABA), glutamic acid decarboxylase 65 antigen (GAD-alum) and proton pump inhibitors (PPI).