Different components of the immune system [e.g., CD4+, CD8+ T cells, Tregs, B cells, dendritic cells (DCs), monocyte/macrophages (Mo/Mφs), natural killer T cells (NKTs)] contribute to autoimmune responses in T1D, complicating efforts to develop successful treatments or a cure that will work across most or all individuals with the disease. This evidence concerns the gene CD4 and type 1 diabetes mellitus.