The alteration of CD26 expression is highly correlated with immune-mediated disorders, such as Diabetic Cardiovascular Disease, Autoimmune Diabetes, Inflammatory Bowel Disease (IBD), acute Graft-versus-Host Disease (GVHD), Coronavirus-related immunological response, Multiple Sclerosis (MS), and Tumor Immune Response. The gene discussed is DPP4; the disease is neoplasm.