Correlation analyses demonstrated that there was a significant negative association between serum OX40 levels and mOX40 expression on CD3+ T cells (r = −0.3629, p = 0.0182) and CD4+ T cells (r = −0.3373, p = 0.0289) in T1D patients (Figure 4). This evidence concerns the gene CD4 and type 1 diabetes mellitus.