Telikani et al. found that sitagliptin in combination with vitamin D3 up-regulated Forkhead box Protein 3 (FoxP3) expression and IL-37 production, and down-regulated Retinoic Acid Receptor (RAR)-Related Orphan Receptor gamma t (RORγt), B-Cell Lymphoma 6 (BCL6), Interferon (IFN)-γ, and IL-17 and IL-21 production, in vivo in patients with T2DM [19]. This evidence concerns the gene IL21 and type 2 diabetes mellitus.